Fix spelling error
Fix spelling error

In the method `check_blank_after_last_paragraph`, the word
`paragraph` was misspelled as `paragtaph`.

Nurdok/pep257,jmullan/pep257,farmersez/pydocstyle,GreenSteam/pep257,13steinj/pep257,jayvdb/pep257,bartvm/pep257,tescalada/pydocstyle,Nurdok/pydocstyle,bagelbits/pep257,pombredanne/pep257,codehs/pep257,jbeezley/pep257,PyCQA/pydocstyle,glennmatthews/pep257