golang third party library auto completion is invalid

golang third-party library auto-completion is invalid：

execute the vim-go command :GoInstallBinariescan be repaired，may report an error：

 error message： vim-go: gogetdoc not found. Installing github.com/zmb3/gogetdoc to folder /usr/local/opt/go/libexec/bin
 xxx timeout

possible cause is PATH configuration error，need to add $GOPATH/bin。which is:

 git clone https://github.com/golang/tools $GOPATH/golang.org/x/tools  # Install gotools directly
 export PATH=$GOPATH/bin:$PATH