added bors integration

.github/bors.toml

@@ -0,0 +1,2 @@
+status = ["ci"]
+delete_merged_branches = true

.github/workflows/ci.yml

@@ -47,4 +47,13 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: -- -D warnings
+          args: -- -D warnings
+
+  ci:
+      if: ${{ success() }}
+      # all new jobs must be added to this list
+      needs: [check, fmt, clippy]
+      runs-on: ubuntu-latest
+      steps:
+        - name: CI succeeded
+          run: exit 0