add specific handling for github rate limit errors

[dbaggerman]

Fixes #36

[coveralls]

Pull Request Test Coverage Report for Build 469

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 32.98%

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Totals
Change from base Build 468:	0.0%
Covered Lines:	685
Relevant Lines:	2077

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💛 - Coveralls