Update common Prometheus files

Signed-off-by: prombot <prometheus-team@googlegroups.com>

Author: prombot

Makefile.common

@@ -55,7 +55,7 @@ ifneq ($(shell command -v gotestsum 2> /dev/null),)
 endif
 endif
 
-PROMU_VERSION ?= 0.18.1
+PROMU_VERSION ?= 0.20.0
 PROMU_URL     := https://github.com/prometheus/promu/releases/download/v$(PROMU_VERSION)/promu-$(PROMU_VERSION).$(GO_BUILD_PLATFORM).tar.gz
 
 SKIP_GOLANGCI_LINT :=