fix detail

Author: fchapoton

src/sage/combinat/words/word_generators.py

@@ -228,7 +228,7 @@ def __init__(self, p, q, alphabet=(0,1), algorithm='cf'):
 
     def markoff_number(self):
         r"""
-        Returns the Markoff number associated to the Christoffel word ``self``.
+        Return the Markoff number associated to the Christoffel word ``self``.
 
         The *Markoff number* of a Christoffel word `w` is `trace(M(w))/3`,
         where `M(w)` is the `2\times 2` matrix obtained by applying the