Add mcgreevy to CONTRIBUTORS.
Add mcgreevy to CONTRIBUTORS.

Change-Id: I8ccb9957d57be6403fb4f128952e1154ca8113f5
Reviewed-on: https://code-review.googlesource.com/2423
Reviewed-by: Glenn Lewis <13a1c799ae0d2ab8fa6a3294896d9a3ccca89794@google.com>

google/google-api-go-client,stephenwithav/google-api-go-client,digideskio/google-api-go-client,80nashi/google-api-go-client,t9nf/google-api-go-client,googleapis/google-api-go-client,googleapis/google-api-go-client,webhost/google-api-go-client,peterkshultz/google-api-go-client,odeke-em/google-api-go-client,krsjoseph/google-api-go-client,likaiwalkman/google-api-go-client,stems/google-api-go-client,google/google-api-go-client,evandbrown/google-api-go-client,skyeunknown084/gmail-api