Node 4 support broken due to mime@2 update.

[rwjblue]

mime@2 was upgrade to in #1003 and subsequently released in 5.4.0.

Since documentation indicates that it supports node >= 4 and mime@2.2.0 requires node >= 6 this was a breaking change.

[tmcw]

Thanks for noting this. We should probably update documentation.js to be node >= 6, given that node v4 is end-of-life on March 30, less than 2 months away.

[rwjblue]

Ya, seems great to bump majors and release with Node >= 6 as a requirement. In the meantime, any objections to reverting #1003 and releasing 5.4.1?