Handle git source not available in Podspec

[UnsafePointer]

According to the Podspec specification, the source can be: git, svn, hg and http. This is a start to support http as a fallback if git is not there, which I believe is the second most used one.

I believe we should also handle in PodSynchronize::Synchronize#update_specs, but I don't have a good solution for the http case, because it basically can be anything.

[coveralls]

Coverage decreased (-2.5%) to 80.214% when pulling f8072cd on Ruenzuo:hande_git_source_not_available_in_podspec into 764b472 on xing:master.

[UnsafePointer]

Sample of this case: google/EarlGrey/EarlGrey.podspec.json#L36-L38

[coveralls]

Coverage decreased (-2.5%) to 80.319% when pulling b36c6a9 on Ruenzuo:hande_git_source_not_available_in_podspec into cabf76b on xing:master.

[pietbrauer]

For me this doesn't work with CrittercismSDK which has the http source https://app.crittercism.com/images/Crittercism_v5_7_0-rc_1.zip 🙄 so the capture for www fails.

@Ruenzuo Any idea on how to solve this?

[UnsafePointer]

Okay so actually doing the whole git source from the http value only makes sense if the host contains "github.com", right? Because we're trying to figure out the git location of the repository to properly mirror it.

So I'll add a check to only do this if the host contains "github.com". Otherwise it'll fall back to the old behaviour, which is to not produce a repository copy of that source.