Missing spec repos on Podfile.lock

[fnxpt]

When updating a Podfile.lock by doing a pod install, sometimes spec repos lose some information.
After poking around I noticed that the issue is on generate_spec_repos on lockfile.rb.
In this function spec_repos are mapped into an Hash, but if the key already exists only the last content is kept.
I'm going to create a PR with the fix, probably not the best ruby code since I don't actively developed in ruby anymore

This can also happen if you have multiple repos with different names but with same url link

[fnxpt]

Hey guys this PR is already approved for almost 1 month... just wanted to understand whats the next step

[fnxpt]

@amorde, do you know when this will be released?