Pswadi/get users json

Describe your PR
Enabling json api for users. Also added email and role to the json output.
Updated gemfile to get latest sawyer gem.

/cc @zendesk/samson 

### References
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### Risks
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yeah, may be I can change it to role_desc, but I feel it is better to put the description rather than just the id / number. i.e. admin vs 1.  However I am okay to remove it, if you feel that is incorrect.