Fixes the reading of dependencies that have spaces in their subspecs' name from Lockfiles

Closes https://github.com/CocoaPods/CocoaPods/issues/2850.
Should've been done with https://github.com/CocoaPods/Core/pull/179.

See http://regexr.com/39uen.
A nice ruby comment to explain this `Regexp` magic in the code would have been nice :wink: