Update docs/rules/1020.md

Co-authored-by: Wes Haggard <[email protected]>

Author: jianyexi

docs/rules/1020.md

@@ -2,7 +2,7 @@
 
 **Description**: Checks whether an existing enum property has added more allowed values from the previous specification. 
 
-**Cause**: This is considered a a breaking change. This change requires new api-version.
+**Cause**: This is considered a breaking change. This change requires new api-version.
 
 **Example**: Enum Property `b` is adding more allowed values without revising api-version.