fix tiny detail only

Author: fchapoton

src/sage/categories/algebras.py

@@ -191,7 +191,7 @@ def has_standard_involution(self):
             try:
                 basis = self.basis()
             except AttributeError:
-                raise AttributeError("Basis is not yet implemented for this algebra.")
+                raise AttributeError("basis is not yet implemented for this algebra")
             try:
                 # TODO: The following code is specific to the quaternion algebra
                 #   and should belong there