docs: fix link to seo constants

Author: woodb

README.md

@@ -171,7 +171,7 @@ Will result in:
 </html>
 ```
 
-A list of prioritized tags and attributes can be found in [constants.js](./blob/master/src/constants.js).
+A list of prioritized tags and attributes can be found in [constants.js](./src/constants.js).
 
 
 ## License