updated period.daysinmonth definition to match period.days_in_month (pandas-dev#47193)

updated daysinmonth definition to match days_in_month

Author: scioccha

pandas/_libs/tslibs/period.pyx

@@ -2256,7 +2256,7 @@ cdef class _Period(PeriodMixin):
     @property
     def daysinmonth(self) -> int:
         """
-        Get the total number of days of the month that the Period falls in.
+        Get the total number of days of the month that this period falls on.
 
         Returns
         -------