add coverage.yaml to github actions (#100)

* add coverage.yaml to github actions

* add all test files to code coverage

.github/workflows/coverage.yml

+name: Coverage
+
+on: [push, pull_request]
+
+jobs:
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup Go
+        uses: actions/setup-go@v1
+        with:
+          go-version: 1.14
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Report results to DeepSource
+        run: |
+          go test -coverprofile=cover.out ./...
+          curl https://deepsource.io/cli | sh
+          ./bin/deepsource report --analyzer test-coverage --key go --value-file ./cover.out
+        env:
+          DEEPSOURCE_DSN: ${{ secrets.DEEPSOURCE_DSN }}
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