Issue with humanizing a RRULE with BYMONTHDAY

[onesneakymofo]

I'm getting an error when I try to humanize a RRULE with BYMONTHDAY.

Error:

> RRule::Rule.new('RRULE:FREQ=MONTHLY;BYMONTHDAY=1').humanize
NameError: undefined local variable or method `_bymonthday' for #<RRule::Humanizer:0x0000000163012908>

The example I'm using is

RRULE:FREQ=MONTHLY;BYMONTHDAY=1

From rrule.js demo:
https://jkbrzt.github.io/rrule/#/rfc/RRULE:FREQ=MONTHLY;BYMONTHDAY=1

It should read:

• every month on the 15th if BYMONTHDAy=15
• every month on the 1st if BYMONTHDAY=1
• every month on the last if BYMONTHDAY=-1

I'll try to fix when I get some time, but if someone else wants to take a crack at it, then by all means.