ci: let bundler-cache: true to install gems

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

Author: kenhys

.github/workflows/linux.yml

@@ -17,10 +17,9 @@ jobs:
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: unit testing
       env:
         CI: true
       run: |
-        gem install bundler rake
-        bundle install --jobs 4 --retry 3
         bundle exec rake test

.github/workflows/macos.yml

@@ -17,10 +17,9 @@ jobs:
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: unit testing
       env:
         CI: true
       run: |
-        gem install bundler rake
-        bundle install --jobs 4 --retry 3
         bundle exec rake test

.github/workflows/windows.yml

@@ -17,10 +17,9 @@ jobs:
     - uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
     - name: unit testing
       env:
         CI: true
       run: |
-        gem install bundler rake
-        bundle install --jobs 4 --retry 3
         bundle exec rake test