eliminated unnecessary cd and failing substitution

Changing the working directory in a sub-subshell
does not change the working directory of the executing
shell.

The substitution was broken for me on _all_ my machines,
so I started looking into the business.

tools/upgrade.sh

-current_path=`pwd`
-current_path=${current_path/ /\\ }
 printf '\033[0;34m%s\033[0m\n' "Upgrading Oh My Zsh"
 cd "$ZSH"
-
 if git pull origin master
 then
   printf '\033[0;32m%s\033[0m\n' '         __                                     __   '
@@ -17,4 +14,3 @@ else
   printf '\033[0;31m%s\033[0m\n' 'There was an error updating. Try again later?'
 fi
 
-cd "$current_path"