reference $HOME in $PROFILE addition rather than hard-coding $NVM_DIR

[michaelficarra]

I recently had to make this change when $HOME changed.

-[ -s "/Users/michael/.nvm/nvm.sh" ] && . "/Users/michael/.nvm/nvm.sh" # This loads nvm
+[ -s "$HOME/.nvm/nvm.sh" ] && . "$HOME/.nvm/nvm.sh" # This loads nvm

Trying to reinstall nvm failed to fix the path differences because it simply looks for nvm.sh in $PROFILE.

[koenpunt]

If we do this, installing in other directories than $HOME will cause issues. Of course this is an exception we can handle in the install script, but it's like this on purpose.
Also checking if the complete path in the .profile is matching is something I thought of just recently.