Add release action

.github/workflows/release.yml

@@ -0,0 +1,29 @@
+name: release
+
+on:
+  push:
+    tags:
+      - 'v*.*.*'
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+
+    env:
+      GEM_HOST_API_KEY: "${{secrets.RUBYGEMS_AUTH_TOKEN}}"
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - uses: ruby/setup-ruby@v1
+
+      - run: bundle install
+
+      - name: publish gem
+        run: |
+          mkdir -p $HOME/.gem
+          touch $HOME/.gem/credentials
+          chmod 0600 $HOME/.gem/credentials
+          printf -- "---\n:rubygems_api_key: ${GEM_HOST_API_KEY}\n" > $HOME/.gem/credentials
+          gem build *.gemspec
+          gem push *.gem