Fix missing import.
Fix missing import.

git-svn-id: acf0ef94bfce630b1a882387fc03ab8593ec6522@56 150532fb-1d5b-0410-a8ab-efec50f980d4

ahaberlie/MetPy,dopplershift/MetPy,Unidata/MetPy,Unidata/MetPy,dopplershift/MetPy,ShawnMurd/MetPy,ahill818/MetPy,jrleeman/MetPy,ahaberlie/MetPy,deeplycloudy/MetPy,jrleeman/MetPy