fix update-translations.py script

Fix little error in condition check of lupdate execution.

Change-Id: I93b3804b6e927dca2165e4575eddfe614d64c9ac
Reviewed-by: Olivier Soldano <olivier.soldano@savoirfairelinux.com>

update-translations.py

@@ -27,8 +27,7 @@ import shutil
 print("== Updating from sources")
 if os.system("lupdate RingWinClient.pro -no-obsolete"):
     print("trying with 'lupdate-qt5'")
-    os.system("lupdate-qt5 RingWinClient.pro -no-obsolete")
-else:
+    if os.system("lupdate-qt5 RingWinClient.pro -no-obsolete"):
         raise RuntimeError("unable to find any suitable lupdate Qt tool on this system. Stopping")
 
 print("== Pushing sources")