update-submodules: use double quotes

Single quotes are not interpreted as a command argument and the
script would not work.

Tuleap: #605
Change-Id: I904838721dd95edbeeaeec394f3a957243973a93

scripts/update-submodules.sh

 #!/usr/bin/env bash
 
-git submodule foreach `git pull origin master`
+git submodule foreach "git pull origin master"
 git add client-android client-gnome client-macosx client-windows daemon lrc
 git commit