[feat] Support PUPPETEER_SKIP_CHROMIUM_DOWNLOAD in npmrc

This patch adds support for PUPPETEER_SKIP_CHROMIUM_DOWNLOAD
variable in npm config.

This aligns the variable with the rest of supported environment variables.

docs/api.md

@@ -151,7 +151,7 @@ Puppeteer is a Node library which provides a high-level API to control Chromium
 Puppeteer looks for certain [environment variables](https://en.wikipedia.org/wiki/Environment_variable) to aid its operations:
 
 - `HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY` - defines HTTP proxy settings that are used to download and run Chromium.
-- `PUPPETEER_SKIP_CHROMIUM_DOWNLOAD` - do not download bundled Chromium during installation step.
+- `PUPPETEER_SKIP_CHROMIUM_DOWNLOAD` - do not download bundled Chromium during installation step. (`puppeteer_skip_chromium_download` in `.npmrc` as same)
 ### class: Puppeteer
 
 Puppeteer module provides a method to launch a Chromium instance.

install.js

@@ -18,6 +18,10 @@ if (process.env.PUPPETEER_SKIP_CHROMIUM_DOWNLOAD) {
   console.log('**INFO** Skipping Chromium download. "PUPPETEER_SKIP_CHROMIUM_DOWNLOAD" environment variable was found.');
   return;
 }
+if (process.env.NPM_CONFIG_PUPPETEER_SKIP_CHROMIUM_DOWNLOAD || process.env.npm_config_puppeteer_skip_chromium_download) {
+  console.log('**INFO** Skipping Chromium download. "PUPPETEER_SKIP_CHROMIUM_DOWNLOAD" was set in npm config.');
+  return;
+}
 
 const Downloader = require('./utils/ChromiumDownloader');
 const platform = Downloader.currentPlatform();