replace gomobile in workflow file (#78)

.github/workflows/main.yml

@@ -29,7 +29,7 @@ jobs:
 
     - name: Install gomobile
       run: |
-        go install golang.org/x/mobile/cmd/gomobile@latest
+        go install github.com/sagernet/gomobile/cmd/gomobile@latest
         export PATH=$PATH:~/go/bin
       
     - name: Setup Java