add cancel step (#27)

* add cancel step

* Update ci.yml

Author: BenjaminAbt

.github/workflows/ci.yml

@@ -1,4 +1,4 @@
-name: NETCore
+name: NET
 
 on:
     push:
@@ -15,6 +15,12 @@ jobs:
     build:
       runs-on: ubuntu-latest
       steps:
+      
+      - name: Cancel previous builds in PR
+        uses: styfle/[email protected]
+        with:
+          access_token: ${{ github.token }}
+          
       - uses: actions/checkout@v2
         with:
           fetch-depth: 0 # avoid shallow clone so nbgv can do its work.