Added LANG shell variable to diff command

I have de_DE.UTF-8 local and the diff command returns some texts (which are parsed in this module) in german language.
To add the shell variable to diff command forces the diff command to use the en_US locale always.
This fixes the command on my Linux machine. I have not tested it on Mac.
@cmuench I'm not sure I understand how this is working.  Is `LANG=en_US` a valid thing to prepend to the `diff` command when running a shell command?