fix build with multi-part $GOPATH
fix build with multi-part $GOPATH

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