Strip trailing slash in alertmanager URL.
Strip trailing slash in alertmanager URL.

Fixes https://github.com/prometheus/prometheus/issues/607

ton31337/prometheus,SaltedMan/prometheus-annotated,SaltedMan/prometheus-annotated,iksaif/prometheus,iksaif/prometheus,Conorbro/prometheus,eliothedeman/prometheus,wxdublin/prometheus,jbdalido/prometheus,gcnonato/prometheus,tattsun/prometheus,dsymonds/prometheus,trigrass2/prometheus,jmcfarlane/prometheus,mtanda/prometheus,wrouesnel/prometheus,rajthilakmca/prometheus,tomwilkie/prometheus,Dieterbe/prometheus,prometheus/prometheus,gcnonato/prometheus,alileza/prometheus,msiebuhr/prometheus,prasincs/prometheus,ton31337/prometheus,cit-lab/prometheus,bluecmd/prometheus,amorken/prometheus,flier/prometheus,fabric8io/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,laushinka/prometheus,AlekSi/prometheus,amorken/prometheus,prometheus/prometheus,gcnonato/prometheus,thachmai/prometheus,prometheus/prometheus,jmcfarlane/prometheus,cit-lab/prometheus,abhishekamralkar/prometheus,eliothedeman/prometheus,dmilstein/prometheus,dln/prometheus,prasincs/prometheus,alileza/prometheus,prometheus/prometheus,brancz/prometheus,gottwald/prometheus,Colstuwjx/prometheus,kangwoo/prometheus,trigrass2/prometheus,AlekSi/prometheus,nicr9/prometheus,brancz/prometheus,smyrman/prometheus,msiebuhr/prometheus,adamron1/prometheus,agaoglu/prometheus,adamron1/prometheus,wndhydrnt/prometheus,alileza/prometheus,dln/prometheus,adamron1/prometheus,yanghongkjxy/prometheus,adamron1/prometheus,AlekSi/prometheus,gesellix/prometheus,rajthilakmca/prometheus,dln/prometheus,dpatel06/prometheus,PrFalken/prometheus,dln/prometheus,gesellix/prometheus,SaltedMan/prometheus-annotated,sudhi-vm/prometheus,Conorbro/prometheus,smyrman/prometheus,keegancsmith/prometheus,JavierZunzunegui/prometheus,yanghongkjxy/prometheus,agaoglu/prometheus,jimmidyson/prometheus,iksaif/prometheus,prometheus/prometheus,keegancsmith/prometheus,dalanlan/prometheus,bluecmd/prometheus,gesellix/prometheus,datajet-io/prometheus,kzittritsch/prometheus,tomwilkie/prometheus,GoogleCloudPlatform/prometheus,fabric8io/prometheus,fabric8io/prometheus,cit-lab/prometheus,laushinka/prometheus,RobertKielty/prometheus,dmilstein/prometheus,prasincs/prometheus,gottwald/prometheus,wndhydrnt/prometheus,Gouthamve/prometheus,mrwacky42/prometheus,RobertKielty/prometheus,Gouthamve/prometheus,eliothedeman/prometheus,Colstuwjx/prometheus,dpatel06/prometheus,flier/prometheus,Conorbro/prometheus,nicr9/prometheus,nicr9/prometheus,PrFalken/prometheus,sudhi-vm/prometheus,sudhi-vm/prometheus,dmilstein/prometheus,ton31337/prometheus,agaoglu/prometheus,smyrman/prometheus,laushinka/prometheus,rajthilakmca/prometheus,dsymonds/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,sudhi-vm/prometheus,keegancsmith/prometheus,kzittritsch/prometheus,alileza/prometheus,q3k/prometheus,dmilstein/prometheus,mtanda/prometheus,thachmai/prometheus,keegancsmith/prometheus,cit-lab/prometheus,jbdalido/prometheus,bluecmd/prometheus,hustbill/prometheus,flier/prometheus,jimmidyson/prometheus,trigrass2/prometheus,fabxc/prometheus,robbiet480/prometheus,msiebuhr/prometheus,amorken/prometheus,rajthilakmca/prometheus,gottwald/prometheus,AlekSi/prometheus,trigrass2/prometheus,thachmai/prometheus,RobertKielty/prometheus,q3k/prometheus,dalanlan/prometheus,wxdublin/prometheus,wndhydrnt/prometheus,kzittritsch/prometheus,tattsun/prometheus,kzittritsch/prometheus,brancz/prometheus,eliothedeman/prometheus,jbdalido/prometheus,tattsun/prometheus,kangwoo/prometheus,jmcfarlane/prometheus,fabric8io/prometheus,dsymonds/prometheus,mtanda/prometheus,hustbill/prometheus,GoogleCloudPlatform/prometheus,fabxc/prometheus,Stackdriver/stackdriver-prometheus,dalanlan/prometheus,jimmidyson/prometheus,abhishekamralkar/prometheus,laushinka/prometheus,alileza/prometheus,dsymonds/prometheus,gesellix/prometheus,wrouesnel/prometheus,slok/prometheus,prasincs/prometheus,gottwald/prometheus,brancz/prometheus,fabxc/prometheus,RobertKielty/prometheus,Colstuwjx/prometheus,Gouthamve/prometheus,q3k/prometheus,slok/prometheus,ton31337/prometheus,Dieterbe/prometheus,dpatel06/prometheus,q3k/prometheus,msiebuhr/prometheus,agaoglu/prometheus,robbiet480/prometheus,thachmai/prometheus,fabxc/prometheus,datajet-io/prometheus,abhishekamralkar/prometheus,slok/prometheus,mrwacky42/prometheus,robbiet480/prometheus,tattsun/prometheus,keegancsmith/prometheus,abhishekamralkar/prometheus,JavierZunzunegui/prometheus,Colstuwjx/prometheus,kangwoo/prometheus,slok/prometheus,PrFalken/prometheus,Conorbro/prometheus,hustbill/prometheus,hustbill/prometheus,Stackdriver/stackdriver-prometheus,datajet-io/prometheus,robbiet480/prometheus,mrwacky42/prometheus,smyrman/prometheus,wrouesnel/prometheus,datajet-io/prometheus,PrFalken/prometheus,mtanda/prometheus,wrouesnel/prometheus,wxdublin/prometheus,yanghongkjxy/prometheus,JavierZunzunegui/prometheus,bluecmd/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,jmcfarlane/prometheus,amorken/prometheus,yanghongkjxy/prometheus,gcnonato/prometheus,tomwilkie/prometheus,Stackdriver/stackdriver-prometheus,SaltedMan/prometheus-annotated,tomwilkie/prometheus,iksaif/prometheus,JavierZunzunegui/prometheus,Dieterbe/prometheus,jbdalido/prometheus