Increase timeout of metacheck from 120 to 300s

Makefile

@@ -51,7 +51,7 @@ gometalint: ## Run every linter ever
 	# gotype and gotypex are disabled because they don't pass on CI and https://github.com/alecthomas/gometalinter/issues/206
 	# gocyclo is temporarily disabled because we don't pass it right now
 	# golint is temporarily disabled because we need to add comments everywhere first
-	gometalinter --disable gotype --disable gotypex --disable=gocyclo --disable golint --enable=megacheck --enable=unparam --deadline=120s --vendor -t --line-length=120 $$(find . -type f -name '*.go' ! -path "./vendor/*" ! -path "./server/static/bindata_assetfs.go" ! -path "**/mocks/*" | xargs -I '{}' dirname '{}' | sort -u)
+	gometalinter --disable gotype --disable gotypex --disable=gocyclo --disable golint --enable=megacheck --enable=unparam --deadline=300s --vendor -t --line-length=120 $$(find . -type f -name '*.go' ! -path "./vendor/*" ! -path "./server/static/bindata_assetfs.go" ! -path "**/mocks/*" | xargs -I '{}' dirname '{}' | sort -u)
 
 gometalint-install: ## Install gometalint
 	go get -u github.com/alecthomas/gometalinter