Allow the usage of json ~> 1.8.0 as that is required for the twitter gem to work.

The original author has already made this change:
https://github.com/liangzan/contacts/commit/569c356765e5c15c6a1bb9297a6fe1cf19ff56e8
Merge pull request #1 from anshulm/patch-1

Allow the usage of json ~> 1.8.0 as that is required for the twitter gem...