Fix build for people without $GOPATH/bin in $PATH.
Fix build for people without $GOPATH/bin in $PATH.

slok/prometheus,brancz/prometheus,Gouthamve/prometheus,yanghongkjxy/prometheus,SaltedMan/prometheus-annotated,GoogleCloudPlatform/prometheus,yanghongkjxy/prometheus,PrFalken/prometheus,gottwald/prometheus,JavierZunzunegui/prometheus,msiebuhr/prometheus,sudhi-vm/prometheus,agaoglu/prometheus,datajet-io/prometheus,kangwoo/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,tomwilkie/prometheus,AlekSi/prometheus,brancz/prometheus,Colstuwjx/prometheus,Colstuwjx/prometheus,gottwald/prometheus,kangwoo/prometheus,JavierZunzunegui/prometheus,AlekSi/prometheus,adamron1/prometheus,amorken/prometheus,JavierZunzunegui/prometheus,alileza/prometheus,prometheus/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,kzittritsch/prometheus,Conorbro/prometheus,agaoglu/prometheus,prometheus/prometheus,keegancsmith/prometheus,adamron1/prometheus,tomwilkie/prometheus,dmilstein/prometheus,dsymonds/prometheus,dsymonds/prometheus,msiebuhr/prometheus,sudhi-vm/prometheus,GoogleCloudPlatform/prometheus,JavierZunzunegui/prometheus,dsymonds/prometheus,tattsun/prometheus,gottwald/prometheus,keegancsmith/prometheus,prometheus/prometheus,tomwilkie/prometheus,dmilstein/prometheus,Conorbro/prometheus,prometheus/prometheus,keegancsmith/prometheus,dmilstein/prometheus,alileza/prometheus,kzittritsch/prometheus,yanghongkjxy/prometheus,sudhi-vm/prometheus,msiebuhr/prometheus,alileza/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,ton31337/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,dsymonds/prometheus,kzittritsch/prometheus,AlekSi/prometheus,slok/prometheus,slok/prometheus,kzittritsch/prometheus,msiebuhr/prometheus,dmilstein/prometheus,PrFalken/prometheus,GoogleCloudPlatform/prometheus,amorken/prometheus,agaoglu/prometheus,Stackdriver/stackdriver-prometheus,Stackdriver/stackdriver-prometheus,tattsun/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,PrFalken/prometheus,Colstuwjx/prometheus,brancz/prometheus,Colstuwjx/prometheus,brancz/prometheus,SaltedMan/prometheus-annotated,datajet-io/prometheus,alileza/prometheus,Gouthamve/prometheus,sudhi-vm/prometheus,agaoglu/prometheus,ton31337/prometheus,amorken/prometheus,AlekSi/prometheus,datajet-io/prometheus,adamron1/prometheus,Conorbro/prometheus,alileza/prometheus,yanghongkjxy/prometheus,SaltedMan/prometheus-annotated,ton31337/prometheus,PrFalken/prometheus,Conorbro/prometheus,tomwilkie/prometheus,datajet-io/prometheus,slok/prometheus,gottwald/prometheus,SaltedMan/prometheus-annotated,adamron1/prometheus,kangwoo/prometheus,ton31337/prometheus,tattsun/prometheus,amorken/prometheus,tattsun/prometheus