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Here's the formatting list I go off of. This is from the docs for 2.1.3. According to this you would want %-m:
Date (Year, Month, Day):
%Y - Year with century (can be negative, 4 digits at least)
-0001, 0000, 1995, 2009, 14292, etc.
%C - year / 100 (rounded down such as 20 in 2009)
%y - year % 100 (00..99)
%m - Month of the year, zero-padded (01..12)
%_m blank-padded ( 1..12)
%-m no-padded (1..12)
%B - The full month name (``January'')
%^B uppercased (``JANUARY'')
%b - The abbreviated month name (``Jan'')
%^b uppercased (``JAN'')
%h - Equivalent to %b
%d - Day of the month, zero-padded (01..31)
%-d no-padded (1..31)
%e - Day of the month, blank-padded ( 1..31)
%j - Day of the year (001..366)
Time (Hour, Minute, Second, Subsecond):
%H - Hour of the day, 24-hour clock, zero-padded (00..23)
%k - Hour of the day, 24-hour clock, blank-padded ( 0..23)
%I - Hour of the day, 12-hour clock, zero-padded (01..12)
%l - Hour of the day, 12-hour clock, blank-padded ( 1..12)
%P - Meridian indicator, lowercase (``am'' or ``pm'')
%p - Meridian indicator, uppercase (``AM'' or ``PM'')
%M - Minute of the hour (00..59)
%S - Second of the minute (00..60)
%L - Millisecond of the second (000..999)
The digits under millisecond are truncated to not produce 1000.
%N - Fractional seconds digits, default is 9 digits (nanosecond)
%3N millisecond (3 digits)
%6N microsecond (6 digits)
%9N nanosecond (9 digits)
%12N picosecond (12 digits)
%15N femtosecond (15 digits)
%18N attosecond (18 digits)
%21N zeptosecond (21 digits)
%24N yoctosecond (24 digits)
The digits under the specified length are truncated to avoid
carry up.
Time zone:
%z - Time zone as hour and minute offset from UTC (e.g. +0900)
%:z - hour and minute offset from UTC with a colo