Use GH Actions as the only CI

.github/workflows/ci.yml

-name: Simple CI
+name: CI
 
-on: [pull_request]
+on:
+  # Trigger the workflow on push or pull request,
+  # but only for the master branch
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
 
 jobs:
-  run-ci:
-    name: Build
-    runs-on: ubuntu-latest
+  build-linux:
+    name: Linux
+    runs-on: ubuntu-18.04
     steps:
     - uses: actions/checkout@v2
     - uses: actions/setup-node@v1
       with:
         node-version: '12.x'
-    - run: sudo apt-get install libx11-dev zlib1g-dev libpng-dev libxtst-dev
-    - run: npm install
-    - run: npm run lint
+    - name: Install dependencies
+      run: sudo apt-get install libx11-dev zlib1g-dev libpng-dev libxtst-dev
+    - name: Build it
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        npm install
+        npm run dist
+  build-mac:
+    name: macOS
+    runs-on: macos-10.15
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-node@v1
+      with:
+        node-version: '12.x'
+    - name: Fixup Xcode
+      # https://github.com/actions/virtual-environments/issues/2557
+      run: |
+        sudo xcode-select -s "/Applications/Xcode_12.4.app"
+        sudo rm -Rf /Library/Developer/CommandLineTools/SDKs/*
+    - name: Build it
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        npm install
+        npm run lint
+        npm run dist
+  build-windows:
+    name: Windows
+    runs-on: windows-2019
+    steps:
+    - uses: actions/checkout@v2
+    - uses: actions/setup-node@v1
+      with:
+        node-version: '12.x'
+    - name: Build it
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      run: |
+        npm install
+        npm run dist

.travis.yml

-matrix:
-  include:
-    - os: osx
-      osx_image: xcode12.4
-      language: node_js
-      node_js: '12'
-
-    - os: linux
-      dist: bionic
-      sudo: true
-      language: node_js
-      node_js: '12'
-      addons:
-        apt:
-          packages:
-            - libx11-dev
-            - zlib1g-dev
-            - libpng-dev
-            - libxtst-dev
-
-script:
-  - npm run dist

appveyor.yml

-image: Visual Studio 2017
-
-platform:
-  - x64
-
-cache:
-  - node_modules
-  - '%USERPROFILE%\.electron'
-
-install:
-  - ps: Install-Product node 12 x64
-  - npm install
-
-build_script:
-  - npm run dist
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