[meld] maint.py: Fix test invocation; we now use py.test helpers, etc.

[Kai Willadsen <kaiw src gnome org>]

commit 71ed611b85e88d23354ee8b581f7afa75c8787e2
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Sun Dec 18 07:38:30 2016 +1000

    maint.py: Fix test invocation; we now use py.test helpers, etc.

 maint.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/maint.py b/maint.py
index 3b44429..5bc43ba 100755
--- a/maint.py
+++ b/maint.py
@@ -296,7 +296,7 @@ def cli():
 
 @cli.command()
 def test():
-    cmd = ['python', '-m', 'unittest', 'discover']
+    cmd = ['py.test-3', 'test/']
     call_with_output(cmd, echo_stdout=True)