Make "New Message!" notification string more consistent with guidelines

Fixes #4758
Closes #4759
// FREEBIE

res/values/strings.xml

@@ -589,7 +589,7 @@
 
     <!-- SingleRecipientNotificationBuilder -->
     <string name="SingleRecipientNotificationBuilder_signal">Signal</string>
-    <string name="SingleRecipientNotificationBuilder_new_message">New Message!</string>
+    <string name="SingleRecipientNotificationBuilder_new_message">New message</string>
 
     <!-- attachment_type_selector -->
     <string name="attachment_type_selector__image">Image</string>