Right version number in the README

Author: PeterJCLaw

README.md

@@ -20,5 +20,5 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: PeterJCLaw/srcomp-validate-action@v0.1
+      - uses: PeterJCLaw/srcomp-validate-action@v0.3
 ```