Switched to GitHub Actions for ESLint

This commit changes the repository from using @travis-ci to GitHub @actions in order to run ESLint on the source code.

.github/workflows/eslint.yml

@@ -0,0 +1,37 @@
+# This is a basic workflow to help you get started with Actions
+
+name: ESLint Format Checker
+
+# Controls when the action will run. Triggers the workflow on push or pull request
+# events but only for the master branch
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: Setup Node.js environment
+        uses: actions/setup-node@v2.1.1
+        with:
+          # Set always-auth in npmrc
+          always-auth: true # optional, default is false
+          # Version Spec of the version to use.  Examples: 12.x, 10.15.1, >=10.15.0
+          node-version: lts # optional
+
+      - name: Install dependencies
+        run: yarn --frozen-lockfile
+
+      - name: Run ESLint
+        run: npx eslint