Show a notification for all builds > 30 sec.

The 300 second threshold was originally from the Gecko/Firefox build system.
It doesn't fit Servo builds, which are shorter, and often hover right around
the 300 second mark (making the notification unpredictable).

python/servo/build_commands.py

@@ -19,7 +19,7 @@ def is_headless_build():
 
 # Function to generate desktop notification once build is completed & limit exceeded!
 def notify(elapsed):
-    if elapsed < 300:
+    if elapsed < 30:
         return
 
     if sys.platform.startswith('linux'):