Update build.yml (#9)

Author: AideTechBot

.github/workflows/build.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v2
     - name: configure
       run: mkdir build && cd build && cmake -DCMAKE_CXX_FLAGS="-Werror" ..
     - name: build