core (constants): fixed Flatpak config path:

trailing "/" was missing in flatpak config path, resulting in the configuration not being read properly on this platform.

sat/core/constants.py

@@ -221,7 +221,7 @@ class Const(object):
             if os.getenv('FLATPAK_ID'):
                 # for Flatpak, the conf can't be set in /etc or $HOME, so we have
                 # to add /app
-                CONFIG_PATHS.append('/app')
+                CONFIG_PATHS.append('/app/')
 
             ## Configuration ##
             DEFAULT_CONFIG = {