DOC: Fix a typo in documentation for qyear
This fixes a typo that I ran across in the [documentation](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.Period.qyear.html?highlight=qyear#pandas.Period.qyear). This change corrects the wording to match the given example that is just below.
Great, thanks @bjcubsfan 