Fix module_cmd finding for zsh

[EmreAtes]

I'm running spack on a system with zsh and the module function is as follows:

$ typeset -f module | envsubst
module () {
	eval `/usr/local/Modules/3.2.10/bin/modulecmd zsh $*`
}

The current regex cannot process this.

[EmreAtes]

I added the universal_newlines parameter in the last commit, because without the parameter popen returns a byte-string, and re doesn't work with byte strings if the search string is not a byte string.