Update github.com/prometheus/client_golang dep

Update to the latest version which had a breaking change on the process
collector func. Following the comment on it it's just a matter of having
`NewProcessCollector(ProcessCollectorOpts{})`

1 files changed, 1 insertions, 2 deletions

diff --git a/Gopkg.toml b/Gopkg.toml
index 93d62762..ff80de01 100644
--- a/Gopkg.toml
+++ b/Gopkg.toml
@@ -89,8 +89,7 @@ ignored = ["test", "appengine"]
 
 [[constraint]]
   name = "github.com/prometheus/client_golang"
-  # version = "0.8.0"
-  revision = "334af0119a8f8fb6af5bb950d535c482cac7f836"
+  version = "0.9.0"
 
 [[constraint]]
   name = "github.com/stretchr/testify"