Adjust wording in cmake message when prometheous cannot be found. (#1418)

src/apps/relay/CMakeLists.txt

@@ -118,7 +118,7 @@ if(Prometheus_FOUND)
     list(APPEND turnserver_LIBS ${Prometheus_LIBRARIES})
     list(APPEND turnserver_include_dirs ${Prometheus_INCLUDE_DIRS})
 else()
-    message(AUTHOR_WARNING "Don't find prometheus. please install "
+    message(AUTHOR_WARNING "Could not find prometheus. Please install "
         "prom, promhttp, microhttpd, and set Prometheus_ROOT. "
         "See docs/Prometheus.md")
     list(APPEND turnserver_DEFINED TURN_NO_PROMETHEUS)