DOC: Make method incorrect.

Scott Sanderson · Scott Sanderson · commit 4d995707dde0 · 2018-04-21T23:04:16.000-04:00
diff --git a/docs/errors.rst b/docs/errors.rst
@@ -72,7 +72,7 @@ Implementations must define interface methods with compatible signatures:
        def prove(self, lemma):
            print("That's almost a theorem, right?")
 
-       def calculate(self, x, y, z):
+       def calculate(self, x, y):
            return x + y
 
 ::
