doc: update repo url in license file

[jblz]

Since the project was moved to https://github.com/nodejs/node, this changes the LICENSE file to direct readers there instead of https://github.com/joyent/node (which redirects to a page saying the project has been moved).

Checklist

• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc

[mscdex]

s/chanegs/changes/ in commit message

[richardlau]

I'm not sure that this should be changed; it's specifically referring to the code that came from Joyent (i.e. pre-convergence) for which a different copyright attribution applies (see nodejs/TSC#174).

cc @jasnell

[BridgeAR]

I think there is a general agreement that this should stay as it is.

@jblz thanks a lot for your contribution anyway! I am sorry your change could not get in.

[jblz]

No worries. Thanks for following up :)