chore: switch to npm from yarn (puppeteer#1878)

This patch:
- migrates CI to use NPM
- drops lockfiles (`yarn.lock`). Lockfiles are ignored by package
  managers when the package is installed as a dependency, so this makes CI closer to the 
  installation our clients run.

.appveyor.yml

@@ -7,11 +7,11 @@ build: off
 
 install:
   - ps: Install-Product node $env:nodejs_version
-  - yarn install
+  - npm install
   - if "%nodejs_version%" == "7" (
-      yarn run lint &&
-      yarn run coverage  &&
-      yarn run test-doclint
+      npm run lint &&
+      npm run coverage  &&
+      npm run test-doclint
     ) else (
-      yarn run unit-node6
+      npm run unit-node6
     )

.gitignore

@@ -8,4 +8,5 @@
 *.pyc
 .vscode
 package-lock.json
+yarn.lock
 /node6

.travis.yml

@@ -6,28 +6,24 @@ addons:
       # This is required to run new chrome on old trusty
       - libnss3
 cache:
-  yarn: true
   directories:
     - node_modules
 # allow headful tests
 before_install:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"
-install:
-  - yarn install
-  # puppeteer's install script downloads Chrome
 script:
-  - 'if [ "$NODE7" = "true" ]; then yarn run lint; fi'
-  - 'if [ "$NODE7" = "true" ]; then yarn run coverage; fi'
-  - 'if [ "$NODE7" = "true" ]; then yarn run test-doclint; fi'
-  - 'if [ "$NODE6" = "true" ]; then yarn run unit-node6; fi'
+  - 'if [ "$NODE7" = "true" ]; then npm run lint; fi'
+  - 'if [ "$NODE7" = "true" ]; then npm run coverage; fi'
+  - 'if [ "$NODE7" = "true" ]; then npm run test-doclint; fi'
+  - 'if [ "$NODE6" = "true" ]; then npm run unit-node6; fi'
 jobs:
   include:
     - node_js: "7.6.0"
       env: NODE7=true
     - node_js: "6.4.0"
       env: NODE6=true
-before_deploy: "yarn run apply-next-version"
+before_deploy: "npm run apply-next-version"
 deploy:
   provider: npm
   email: [email protected]

README.md

@@ -32,8 +32,8 @@ Give it a spin: https://try-puppeteer.appspot.com/
 
 To use Puppeteer in your project, run:
 ```
-yarn add puppeteer
-# or "npm i puppeteer"
+npm i --save puppeteer
+# or "yarn add puppeteer"
 ```
 
 Note: When you install Puppeteer, it downloads a recent version of Chromium (~71Mb Mac, ~90Mb Linux, ~110Mb Win) that is guaranteed to work with the API. To skip the download, see [Environment variables](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#environment-variables).
@@ -131,7 +131,7 @@ const browser = await puppeteer.launch({executablePath: '/path/to/Chrome'});
 
 See [`Puppeteer.launch()`](https://github.com/GoogleChrome/puppeteer/blob/master/docs/api.md#puppeteerlaunchoptions) for more information.
 
-See [`this article`](https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/) for a description 
+See [`this article`](https://www.howtogeek.com/202825/what%E2%80%99s-the-difference-between-chromium-and-chrome/) for a description
 of the differences between Chromium and Chrome. [`This article`](https://chromium.googlesource.com/chromium/src/+/lkcr/docs/chromium_browser_vs_google_chrome.md) describes some differences for Linux users.
 
 **3. Creates a fresh user profile**

docs/troubleshooting.md

@@ -130,7 +130,7 @@ RUN chmod +x /usr/local/bin/dumb-init
 # ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD true
 
 # Install puppeteer so it's available in the container.
-RUN yarn add puppeteer
+RUN npm i puppeteer
 
 # Add user so we don't need --no-sandbox.
 RUN groupadd -r pptruser && useradd -r -g pptruser -G audio,video pptruser \
@@ -227,7 +227,7 @@ Seeing other weird errors when launching Chrome? Try running your container
 with `docker run --cap-add=SYS_ADMIN` when developing locally. Since the Dockerfile
 adds a `pptr` user as a non-privileged user, it may not have all the necessary privileges.
 
-[dumb-init](https://github.com/Yelp/dumb-init) is worth checking out if you're 
+[dumb-init](https://github.com/Yelp/dumb-init) is worth checking out if you're
 experiencing a lot of zombies Chrome processes sticking around. There's special
 treatment for processes with PID=1, which makes it hard to terminate Chrome
 properly in some cases (e.g. in Docker).

examples/README.md

@@ -1,6 +1,6 @@
 # Running the examples
 
-Assuming you have a checkout of the Puppeteer repo and have run yarn (or npm i) to install the dependencies, the examples can be run from the root folder like so:
+Assuming you have a checkout of the Puppeteer repo and have run npm i (or yarn) to install the dependencies, the examples can be run from the root folder like so:
 
 ```sh
 NODE_PATH=../ node examples/search.js

lib/Launcher.js

@@ -92,7 +92,7 @@ class Launcher {
     if (typeof chromeExecutable !== 'string') {
       const downloader = Downloader.createDefault();
       const revisionInfo = downloader.revisionInfo(downloader.currentPlatform(), ChromiumRevision);
-      console.assert(revisionInfo.downloaded, `Chromium revision is not downloaded. Run "yarn install" or "npm install"`);
+      console.assert(revisionInfo.downloaded, `Chromium revision is not downloaded. Run "npm install" or "yarn install"`);
       chromeExecutable = revisionInfo.executablePath;
     }
     if (Array.isArray(options.args))