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.
Being a RegEx lover and master, I was aware of the `x` option, even if I rarely use it as I speak RegExp fluently :laughing: But that's not the case for everyone so indeed that could have been used here.