Fix node_modules path

In some cases we need to install this hooks in nested repositories. This request fix bug with this case
This line's goal is returning a path of a "node_modules" path. The code analysis:
 * pwd - print this path,
 * cd `dirname $0` - change working directory to the script's one,
 * sed 's/\(.*\/node_modules\).*$/\1/' - strip the part after the "node_modules"