Merge branch 'release/1.1.7' into develop
Make sure globalSuffix is undefined when not used.

Otherwise, StatsD will create metrics like '.../metric/rate/.wsp'
instead of '.../metric/rate.wsp'.
Merge pull request #32 from mailgun/global-suffix-undefined

Make sure globalSuffix is undefined when not used.
v1.1.8
Merge branch 'release/1.1.8'