Makes the time zone optional in the date filter
Problem with the current R_ISO8601_STR regex was that the time was optional, but the zone was not.
This results in the filter not formatting local date times, which it could easily do.
For example:
2012-08-30 -> formatted
2012-08-30T06:06:06.123Z -> formatted
2012-08-30T06:06:06.123 -> NOT formatted
A simple change in the regex fixes this. Arguably this is closer to the ISO8601 spec which specifies
local dates being in the "current time zone" and not requiring a Z. In any case it behaves more like
a user would expect.
9473780e77