Add period to compiler flag description to match others

src/compiler/diagnosticMessages.json

@@ -4939,7 +4939,7 @@
         "category": "Message",
         "code": 95075
     },
-    "Allow accessing UMD globals from modules": {
+    "Allow accessing UMD globals from modules.": {
         "category": "Message",
         "code": 95076
     }