v4.0.0

Breaking:

• Require Node.js 6. b5a583d

Other:

• Add unitCount option. (#29) 4717127
• Add option to format microseconds and nanoseconds. (#25) 0950e70
• Fix {secDecimalDigits: 0} rounding rollover issue. (#27) 7602f88

v3.2.0...v4.0.0