Use GH Actions instead of Travis (#40)

.github/workflows/format.yml

@@ -0,0 +1,26 @@
+name: Clang format
+
+on: [pull_request]
+
+jobs:
+  clang-format-8:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        ref: ${{ github.event.pull_request.head.sha }}
+    - name: Run clang-foramt on changed files
+      run: |
+        set -x
+        git fetch origin ${{ github.event.pull_request.base.ref }}
+        git fetch origin pull/${{ github.event.pull_request.number }}/head:${{ github.event.pull_request.head.ref }}
+        BASE_COMMIT=$(git rev-parse ${{ github.event.pull_request.base.sha }})
+        COMMIT_FILES=$(git diff --name-only ${BASE_COMMIT} | grep -i -v LinkDef)
+        RESULT_OUTPUT=$(git-clang-format-8 --commit ${BASE_COMMIT} --diff --binary $(which clang-format-8) ${COMMIT_FILES})
+        if [ "$RESULT_OUTPUT" == "no modified files to format" ] || [ "$RESULT_OUTPUT" == "clang-format did not modify any files" ]; then
+          exit 0
+        else
+          git-clang-format-8 --commit $BASE_COMMIT --diff --binary $(which clang-format-8)
+          echo "$RESULT_OUTPUT"
+          exit 1
+        fi