chore(etc): add option dash to upstart config

etc/linux-upstart/user/syncthing.conf

@@ -18,4 +18,4 @@ env STNORESTART=yes
 respawn
 
 # the syncthing command Upstart is to execute when it is started up
-exec $SYNCTHING_EXE -no-browser
+exec $SYNCTHING_EXE --no-browser