Bug in offset when parsing iso8601 date/time

[dotdoom]

There's an error in regex used to parse iso8601:

https://github.com/baalexander/node-xmlrpc/blob/d9c88c4185e16637ed5a22c1b91c80e958e8d69e/lib/date_formatter.js#L32

\. is treated by JavaScript as ., resulting in "any character" match, rather than "dot". A simple fix would be to replace \. with [.] which is agnostic of escapes. This also needs a test.