internal/worker: fix staticcheck error

Fix staticcheck error:

internal/worker/server.go:491:10: error strings should not be capitalized (ST1005)

Change-Id: I7307e897fc7dc6e77075aca96f1fd15a5a338a33
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/768314
Reviewed-by: Jonathan Amsterdam <jba@google.com>

internal/worker/server.go

@@ -488,7 +488,7 @@ func (s *Server) handleReprocess(w http.ResponseWriter, r *http.Request) error {
 
 func (s *Server) clearCache(w http.ResponseWriter, r *http.Request) error {
 	if s.redisCacheClient == nil {
-		return errors.New("Redis cache client is not configured")
+		return errors.New("redis cache client is not configured")
 	}
 	status := s.redisCacheClient.FlushAll()
 	if status.Err() != nil {