fix: add .exe suffix for windows binaries

Author: menzerath

.github/workflows/build.yml

@@ -23,11 +23,14 @@ jobs:
         uses: actions/setup-go@v2
         with:
           go-version: 1.17
+      - name: decide build file suffix
+        if: ${{ matrix.goos == "windows" }}
+        run: echo "suffix=.exe" >> $GITHUB_ENV
       - name: build project
         env:
           GOOS: ${{ matrix.goos }}
           GOARCH: ${{ matrix.goarch }}
-        run: go build -o build/monstercat_${{ matrix.goos }}_${{ matrix.goarch }} main.go
+        run: go build -o build/monstercat_${{ matrix.goos }}_${{ matrix.goarch }}${{ env.suffix }} main.go
       - name: store binary
         uses: actions/upload-artifact@v2
         with: