Edit docstring.

Author: WaVEV

django_mongodb/compiler.py

@@ -412,7 +412,7 @@ def project_field(column):
             if hasattr(column, "target"):
                 # column is a Col.
                 target = column.target.column
-            # Handle Order by columns as refs columns.
+            # Handle Order By columns as refs columns.
             elif isinstance(column, OrderBy) and isinstance(column.expression, Ref):
                 target = column.expression.refs
             else: