servo: Merge #8024 - Add clarity to warning message about OS X notifications (from tareqak:warning_message_about_os_x_notifications_is_unclear); r=frewsxcv

I made this change with respect to this issue: https://github.com/servo/servo/issues/7840

Source-Repo: https://github.com/servo/servo
Source-Revision: f8ada66919c8fda836b8e33375e82c1ef9059999

servo/python/servo/build_commands.py

@@ -37,7 +37,7 @@ def notify_linux(title, text):
         method = notify_obj.get_dbus_method("Notify", "org.freedesktop.Notifications")
         method(title, 0, "", text, "", [], {"transient": True}, -1)
     except:
-        raise Exception("Please make sure that the Python dbus module is installed!")
+        raise Exception("Optional Python module 'dbus' is not installed.")
 
 
 def notify_win(title, text):
@@ -82,7 +82,7 @@ def notify_darwin(title, text):
         centre = Foundation.NSUserNotificationCenter.defaultUserNotificationCenter()
         centre.scheduleNotification_(note)
     except ImportError:
-        raise Exception("Please make sure that the Python pyobjc module is installed!")
+        raise Exception("Optional Python module 'pyobjc' is not installed.")
 
 
 def notify_build_done(elapsed):