DSL command run will report error after 'brew install X' even when successful

[bwillis]

I ran rockit with this RockitFile :

# command phantomjs required for guard-jasmine
if_command_missing('phantomjs') do
  run "brew install phantomjs"
end

It outputted the following :

➜  cypress git:(XXX) ✗ rockit
brew install phantomjs
required command 'phantomjs' is not available.

But the library was installed successfully.