bower unable to connect to github.com

bower install 遇到错误如下:

bower angular-scenario#>=1.2.*          resolve git://github.com/angular/bower-angular-scenario.git#>=1.2.*
bower bootstrap#~3.1.1                  ECMDERR Failed to execute "git ls-remote --tags --heads git://github.com/twbs/bootstrap.git", exit code of #128

Additional error details:
fatal: unable to connect to github.com:

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