Ruby: Convert to UTC time in ISO 8601 format with millisecond precision, padding of 3.

utc_iso8601_milli.rb

def utc_iso8601_milli(time)
  time.utc.strftime '%FT%T.%LZ'
end

utc_iso8601_milli Time.now
# => "2016-09-02T07:06:18.134Z"

utc_iso8601_milli Time.new(2002, 10, 31, 2, 2, 2, "+05:00") 
# => "2002-10-30T21:02:02.000Z"

# Millisecond with padding of 3. More precise fractions will be truncated:
utc_iso8601_milli Time.new(2016, 5, 24, 15, 29, 0.1239)
# => "2016-05-24T09:59:00.123Z"

utc_iso8601_milli Time.new(2016, 5, 24, 15, 29, 22.1239)
# => "2016-05-24T09:59:22.123Z"

https://ruby-doc.org/core-2.2.2/Time.html
http://idiosyncratic-ruby.com/57-what-the-time.html

utc_iso8601_milli Time.new(2016, 5, 24, 15, 29, 22.0039)
# => "2016-05-24T09:59:22.003Z"

YYYY-MM-DDTHH:MM:SS.MMMZ