Fix install / run issues on Ubuntu

[lloydwatkin]

This fixes issues on Ubuntu 14.04 for myself. Sorry there's no tests but hopefully this is a help towards a solution.

See #483
Fixes #394

[ljharb]

Thanks for the contribution! I'm very hesitant to add OS-specific fixes, especially without tests that can automatically run on that OS.

[lloydwatkin]

I totally see where you are coming from on this. But at least we're
discussing solutions :)

It did occur to me that the second part of the check could be for $HOME
being part of $NVM_DIR.

This makes it no longer OS specific and won't break thinks for anyone.

How would that work for you?

If you could point me at where a test for/like this would live I'd be happy
to take a stab at adding a couple. Presumably set $NVM_DIR to something
'bad' and see that it gets overwritten.

Cheers, Lloyd.

[ljharb]

Unfortunately it'd be perfectly valid for someone to set $NVM_DIR to be something that's not in $HOME.

I'm not sure if it's possible to do an Ubuntu-specific test on Travis - that'd be the difficulty in testing for it.

I'd love to discover why this one OS out of all of them is causing problems, and see if there's a way we could indeed construct a test that would simulate the behavior without having ubuntu.

[ljharb]

Closing this for now - will be happy to reopen if you still have an interest.