[gnome-settings-daemon] power: Fix setting GSD_MOCK envvar

[Bastien Nocera <hadess src gnome org>]

commit 70e3343a7e9f8769f8abd4ccd64c16ab7999a154
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Jan 17 12:04:18 2017 +0100

    power: Fix setting GSD_MOCK envvar
    
    Wrong syntax used, introduced in 5fc7cb64.

 plugins/power/test.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/plugins/power/test.py b/plugins/power/test.py
index 082ad80..a063362 100755
--- a/plugins/power/test.py
+++ b/plugins/power/test.py
@@ -31,7 +31,7 @@ class PowerPluginTest(gsdtestcase.GSDTestCase):
     '''Test the power plugin'''
 
     def setUp(self):
-        os.environ.set('GSD_MOCK', '1')
+        os.environ['GSD_MOCK']='1'
         self.check_logind_gnome_session()
         self.start_logind()
         self.daemon_death_expected = False