nimble publish failed if (local) git default branch name is not master
maybe we should specify the a hard-coded branch name for the temporory repo

```
      Info: Writing access token to file:C:\Users\CodeHz\.nimble\github_api_token
   Success: Verified as codehz
      Info: Waiting 10s to let Github create a fork
    Copying packages fork into: C:\Users\CodeHz\AppData\Local\Temp\nimble-packages-fork
   Updating the fork
       Tip: 1 messages have been suppressed, use --verbose to show them.
     Error: Execution failed with exit code 1
        ... Command: git push https://MASK@github.com/codehz/packages master
        ... Output: error: src refspec master does not match any
        ... error: failed to push some refs to 'git://github.com/codehz/packages'
```