update to octokit 2.1

* replace tests using Hashie::Mash with Sawyer::Resource
* add helper method #sawyer_resource to wrap attrs in a
Sawyer::Resource like Octokit
* Sawyer::Resource uses symbol keys
replace calls to #search_issues with #legacy_search_issues

The v3 search API is not final yet. The old search, which will be
supported in v3.

http://developer.github.com/v3/search/
refactor #find_issue, add private #find_first_issue
lock octokit dependency to patch level
Merge pull request #71 from teeparham/octokit2

update to octokit 2.1