deps: upgrade to npm 2.14.15

Hi! This PR includes three releases!

• https://github.com/npm/npm/releases/tag/v2.14.13
• https://github.com/npm/npm/releases/tag/v2.14.14
• https://github.com/npm/npm/releases/tag/v2.14.15

Relevant changes:

• Lots of doc updates/fixes
• 6051a69 #10685 Fix npm public registry URL in notices.
• #10629 Node can be compiled FIPS-compliant now due to MD5 extraction (it was previously used for non-security purposes)
• nodejs/node-gyp#831 New node-gyp with better *BSD support
• #10532 Clarify that registry.npmjs.org is the default, but that you're free to use the npm CLI with whatever registry you wish. This goes along with previous licensing-related improvements, too.
• 333e118 Better AIX support for node-gyp

Those are the highlights! And to repeat: This does include some of the previously-talked-about licensing changes.

r: @Fishrock123 r: @iarna