Apply suggestions from PR review

Co-authored-by: Ralf Handl <[email protected]>

Author: mikekistler

CONTRIBUTING.md

@@ -54,8 +54,7 @@ The following additional rules should be followed but currently are not enforced
 6. Field values are monospaced in JSON notation: `true`, `false`, `null`, `"header"` (with double-quotes around string values), ...
 7. A combination of fixed field name with example value uses JS notation: `in: "header"`, combining rules 5 and 6
 8. An exception to 5-7 is colloquial use, for example "values of type `array` or `object`" - "type" is not monospaced, so the monospaced values aren't enclosed in double quotes.
-9. "attribute" is only used in the XML context and means "XML attribute"
-10. Use Oxford commas, avoid Shatner commas
+9. Use Oxford commas, avoid Shatner commas
 
 ### Use of "keyword", "field", "property", and "attribute"