Added DataTime object change to the Upgrading Guide

"DateTime fields are now proper `DateTime` objects. Previous versions outputed DateTime fields as 'String' objects."
Merge pull request #346 from StephenOTT/master

Added DataTime object change to the Upgrading Guide
Add documentation for two-factor authentication

The documentation was not super clear on how to use 2FA authentication tokens with 2FA enabled users so this is an addition to the README to clarify that.
Fix typo: Github to GitHub
Merge pull request #348 from jasontruluck/master

Add documentation for two-factor authentication
Check for nil creds when trying to load missing netrc

If there's no netrc defined for this api endpoint, output a warning instead of
throwing a shift error
Merge pull request #349 from catsby/warn_netrc_nil

Rescue from NoMethodError when trying to load missing netrc
v2.6.2
Release 2.6.2
Use a relative path for search requests.

The API endpoint for GitHub Enterprise is located at /api/v3. By setting
the preceding / in the api path it's treating the path as a full path
instead of a relative path.
Merge pull request #350 from benburkert/enterprise-search

Use a relative path for search requests