Fixed incorrect comment for changing $PATH for brew

The current form is incorrect and ends up settings the user's path to /usr/local/bin:$PATH

LS2-00133:~ bovardtiberi$ echo $PATH
/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
LS2-00133:~ bovardtiberi$ export PATH='/usr/local/bin:$PATH'
LS2-00133:~ bovardtiberi$ echo $PATH
/usr/local/bin:$PATH
LS2-00133:~ bovardtiberi$ export PATH='/usr/local/bin':$PATH
LS2-00133:~ bovardtiberi$ echo $PATH
/usr/local/bin:/usr/local/bin:$PATH