Convert specs to RSpec 3 syntax with Transpec

Converted specs to 3 syntax using the Transpec gem. Additionally, updated test in endpoint_spec.rb on Line 108 to check for nil rather than attempting to match on nil.

Author: danielspector

CHANGELOG.md

@@ -10,6 +10,7 @@ Next Release
 
 * [#614](https://github.com/intridea/grape/pull/614): Params with `nil` value are now refused by `RegexpValidator` - [@dm1try](https://github.com/dm1try).
 * [#494](https://github.com/intridea/grape/issues/494): Fixed performance issue with requests carrying a large payload - [@dblock](https://github.com/dblock).
+* [#619](https://github.com/intridea/grape/pull/619): Convert specs to RSpec 3 syntax with Transpec - [@danielspector](https://github.com/danielspector).
 
 0.7.0 (4/2/2013)
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