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.
1. An optional whitespace-char
2. followed by one or more chars that are neither spaces nor `(`
3. optionally followed by a (hard-coded) space + any chars

Not sure it makes sense in that context, but that's how I read the Matrix.