explorer: Use Github Actions for CI (solana-labs#19814)

* explorer: Use Github Actions for CI

* clean up mergify

.github/workflows/explorer.yml

@@ -0,0 +1,34 @@
+name: Explorer
+
+on:
+  push:
+    branches: [ master ]
+    paths:
+      - "explorer/**"
+  pull_request:
+    branches: [ master ]
+    paths:
+      - "explorer/**"
+
+jobs:
+  check-explorer:
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        working-directory: explorer
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-node@v2
+        with:
+          # "node" (v16) is not supported by node-sass yet
+          # https://github.com/sass/node-sass/pull/3090
+          node-version: '14'
+          cache: 'npm'
+          cache-dependency-path: explorer/package-lock.json
+      - run: npm i -g npm@7
+      - run: npm ci
+      - run: npm run format
+      - run: npm run build
+      - run: npm run test

.mergify.yml

@@ -20,6 +20,7 @@ pull_request_rules:
     conditions:
       - status-success=buildkite/solana
       - status-success=Travis CI - Pull Request
+      - status-success=check-explorer
       - status-success=ci-gate
       - label=automerge
       - author≠@dont-squash-my-commits
@@ -31,6 +32,7 @@ pull_request_rules:
     conditions:
       - status-success=buildkite/solana
       - status-success=Travis CI - Pull Request
+      - status-success=check-explorer
       - status-success=ci-gate
       - label=automerge
       - author=@dont-squash-my-commits

.travis.yml

@@ -68,26 +68,6 @@ jobs:
     #  before_install:
     #    - sudo apt-get install libssl-dev libudev-dev
 
-    # explorer pull request
-    - name: "explorer"
-      if: type = pull_request AND branch = master
-
-      language: node_js
-      node_js:
-        - "lts/*"
-
-      cache:
-        directories:
-          - ~/.npm
-
-      before_install:
-        - .travis/affects.sh explorer/ .travis || travis_terminate 0
-        - cd explorer
-
-      script:
-        - npm run build
-        - npm run format
-
     # web3.js pull request
     - name: "web3.js"
       if: type = pull_request AND branch = master