Make compatible dotfiles directory creation for all platforms

[devngl]

Apparently sed command has different implementations depending on the platform, after a few tests in both Mac and GNU the only way I found to make it work is to actually replace said command.

More information can be found at:
https://stackoverflow.com/questions/4247068/sed-command-with-i-option-failing-on-mac-but-works-on-linux

On the other hand the cp -r command wasn't working for me either, looks like the trailing slash is needed (but I don't understand exactly why as it seems Ok without it).

[josecarlosduran]

Hello @devngl, @JavierCane and @rgomezcasas I came here to fork the project and work on this error but I see that you had already a solution

I modify the sed to :

sed -i '' -e "s|XXX_DOTFILES_PATH_XXX|$DOTFILES_PATH|g" "$DOTFILES_PATH/shell/zsh/.zshenv" and it works

I don't know what solution it's better

[rgomezcasas]

@josecarlosduran I prefer with sed as you purposed!

You can create a PR with that change :), but for now I'm merging this!

Thanks to both!!