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
 - Jira link:

### Risks
 - None
Can you add a test for this controller responding with JSON? It looks like scaffholding so easy to remove unless there is a test.