fix doctest

Author: fchapoton

src/sage/categories/finite_coxeter_groups.py

@@ -14,6 +14,7 @@
 from sage.categories.category_with_axiom import CategoryWithAxiom
 from sage.categories.coxeter_groups import CoxeterGroups
 
+
 class FiniteCoxeterGroups(CategoryWithAxiom):
     r"""
     The category of finite Coxeter groups.
@@ -889,7 +890,7 @@ def coxeter_knuth_graph(self):
                 sage: w.coxeter_knuth_graph()
                 Traceback (most recent call last):
                 ...
-                NotImplementedError: This has only been implemented in finite type A so far!
+                NotImplementedError: this has only been implemented in finite type A so far
             """
             from sage.graphs.graph import Graph
             R = [tuple(v) for v in self.reduced_words()]