Fix docstring for Sphinx compatibility.
Fix docstring for Sphinx compatibility.

jmagnusson/wtforms,crast/wtforms,Aaron1992/wtforms,pawl/wtforms,wtforms/wtforms,hsum/wtforms,skytreader/wtforms,subyraman/wtforms,cklein/wtforms,Aaron1992/wtforms,pawl/wtforms,Xender/wtforms