enable Maven cache for Windows too

Author: Vladimir Kotal

.github/workflows/build.yml

@@ -57,6 +57,12 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 11
+    - name: Cache Maven packages
+      uses: actions/cache@v2
+      with:
+        path: ~/.m2
+        key: ${{ runner.os }}-m2-${{ hashFiles('**/pom.xml') }}
+        restore-keys: ${{ runner.os }}-m2
     - name: Install Universal ctags
       run: choco install universal-ctags
     - name: Install Subversion