using fixed version for gomobile ios

Author: jerson

.github/workflows/gomobile.yml

@@ -49,7 +49,8 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-go@v2
         with:
-          go-version: '^1.15'
+          go-version: '1.15.4'
+          # using fixed version due to error: go build runtime/cgo: invalid flag in go:cgo_ldflag: -fembed-bitcode
       - name: Install Gomobile
         run: make gomobile
       - name: Build