Replaces Acorn over Travis CI by ESLint over (Microsoft) GitHub Actions

> See #11, Acorn was great but not sufficient for Mozilla's libPref syntax...

.eslintrc.yml

@@ -0,0 +1,45 @@
+%YAML 1.2
+---
+
+root: true
+
+extends: 'eslint:recommended'
+
+globals:
+  # From <https://searchfox.org/mozilla-central/rev/c938c7416c633639a5c8ce4412be586eefb48005/modules/libpref/parser/src/lib.rs#296>
+  pref: true
+  user_pref: true
+  sticky: true
+  locked: true
+  sticky_pref: true
+
+rules:
+  # Expect a semicolon after each statement.
+  semi:
+    - "error"
+    - "always"
+    -
+      omitLastInOneLineBlock: false
+
+  # As internal code style, don't allow tabulation.
+  no-tabs: "error"
+  # ... nor trailing spaces !
+  no-trailing-spaces: "error"
+
+  # Expect only double-quoted strings.
+  quotes:
+    - "error"
+    - "double"
+
+  # Don't allow whitespace before semicolons.
+  semi-spacing:
+    - "error"
+    -
+      before: false
+
+  # Don't allow irregular whitespace characters in our sheet.
+  no-irregular-whitespace:
+    - "error"
+    -
+      skipStrings: false
+      skipComments: false

.github/workflows/linting.yml

@@ -0,0 +1,17 @@
+---
+name: Linting
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    name: Run ESLint on user.js
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: actions/setup-node@v1
+
+      - run: npm install -g eslint
+      - run: eslint user.js

.travis.yml

@@ -1,8 +0,0 @@
-language: node_js
-node_js:
-  - 'node'
-
-before_script:
-  - npm install -g acorn
-script:
-  - acorn --silent user.js