def merge(base, opts= {})
      logger.info { "Merging #{branches.current.name} with #{base}" }
      args = []
      args << '-s' << opts[:merge_strategy] if opts[:merge_strategy]
      args << base
      return command(:merge, args)
    end
def merge(base, opts= {})
      logger.info { "Merging #{branches.current.name} with #{base}" }
      args = []
      args << '-s' << opts[:merge_strategy] if opts[:merge_strategy]
      args << base
      return command(:merge, args)
    end
`git merge`

 @return [String] the output of 'git merge'