go.mod: Update dependencies

github.com/golang/protobuf v1.5.1 -> v1.5.2
github.com/prometheus/client_golang v1.10.0 -> v1.11.0
github.com/prometheus/common v0.19.0 -> v0.30.0
github.com/prometheus/exporter-toolkit v0.5.1 -> v0.6.1

Signed-off-by: Manuel Rüger <manuel@rueg.eu>

go.mod

@@ -2,12 +2,12 @@ module github.com/prometheus/pushgateway
 
 require (
 	github.com/go-kit/log v0.1.0
-	github.com/golang/protobuf v1.5.1
+	github.com/golang/protobuf v1.5.2
 	github.com/matttproud/golang_protobuf_extensions v1.0.1
-	github.com/prometheus/client_golang v1.10.0
+	github.com/prometheus/client_golang v1.11.0
 	github.com/prometheus/client_model v0.2.0
-	github.com/prometheus/common v0.19.0
-	github.com/prometheus/exporter-toolkit v0.5.1
+	github.com/prometheus/common v0.30.0
+	github.com/prometheus/exporter-toolkit v0.6.1
 	github.com/shurcooL/httpfs v0.0.0-20190707220628-8d4bc4ba7749 // indirect
 	github.com/shurcooL/vfsgen v0.0.0-20200824052919-0d455de96546
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6