Use GitHub Actions instead of Travis CI.

.github/workflows/macos.yml

@@ -0,0 +1,22 @@
+name: macos
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        ruby: [ '2.6.x', '2.5.x', '2.4.x' ]
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up Ruby
+      uses: actions/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+    - name: Set up Bundler
+      run: gem install bundler --no-document
+    - name: Install dependencies
+      run: bundle install
+    - name: Run test
+      run: rake

.github/workflows/ubuntu-rvm.yml

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+name: ubuntu-rvm
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: [ 'ruby-head' ]
+      fail-fast: false
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up RVM
+      run: |
+        curl -sSL https://get.rvm.io | bash
+    - name: Set up Ruby
+      run: |
+        source $HOME/.rvm/scripts/rvm
+        rvm install ${{ matrix.ruby }} --binary
+        rvm --default use ${{ matrix.ruby }}
+    - name: Set up Bundler
+      run: |
+        source $HOME/.rvm/scripts/rvm
+        gem install bundler --no-document
+    - name: Install dependencies
+      run: |
+        source $HOME/.rvm/scripts/rvm
+        bundle install
+    - name: Run test
+      run: |
+        source $HOME/.rvm/scripts/rvm
+        rake

.github/workflows/ubuntu.yml

@@ -0,0 +1,22 @@
+name: ubuntu
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: [ '2.6.x', '2.5.x', '2.4.x' ]
+    steps:
+    - uses: actions/checkout@master
+    - name: Set up Ruby
+      uses: actions/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+    - name: Set up Bundler
+      run: gem install bundler --no-document
+    - name: Install dependencies
+      run: bundle install
+    - name: Run test
+      run: rake