Bump github.com/prometheus/common from 0.10.0 to 0.15.0 (#141)

Bumps [github.com/prometheus/common](https://github.com/prometheus/common) from 0.10.0 to 0.15.0.
- [Release notes](https://github.com/prometheus/common/releases)
- [Commits](prometheus/common@v0.10.0...v0.15.0)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

go.mod

@@ -3,11 +3,8 @@ module github.com/nginxinc/nginx-prometheus-exporter
 go 1.15
 
 require (
-	github.com/golang/protobuf v1.4.2 // indirect
 	github.com/nginxinc/nginx-plus-go-client v0.6.0
-	github.com/prometheus/client_golang v1.6.0
-	github.com/prometheus/common v0.10.0
-	github.com/prometheus/procfs v0.1.3 // indirect
-	golang.org/x/sys v0.0.0-20200615200032-f1bc736245b1 // indirect
+	github.com/prometheus/client_golang v1.7.1
+	github.com/prometheus/common v0.15.0
 	google.golang.org/protobuf v1.24.0 // indirect
 )