Fix grammar

dstansby · web-flow · commit f37aa9cd2f98 · 2020-07-04T11:30:28.000+01:00
diff --git a/lib/matplotlib/category.py b/lib/matplotlib/category.py
@@ -115,7 +115,7 @@ def default_units(data, axis):
     def _validate_unit(unit):
         if not hasattr(unit, '_mapping'):
             raise ValueError(
-                f'Provided unit "{unit}" is not a valid for a categorical '
+                f'Provided unit "{unit}" is not valid for a categorical '
                 'converter, as it does not have a _mapping attribute.')
 
 
