Update reference/tax_classes.v3.yaml

Co-authored-by: Brett Daniels <theromulans@gmail.com>

Author: bc-vincent-zhao

reference/tax_classes.v3.yaml

@@ -58,7 +58,7 @@ paths:
               schema:
                 $ref: '#/components/schemas/TaxClassCollectionEnvelope'
         '400':
-          description: Bad request (e.g. invalid input).
+          description: Bad request (e.g., invalid input).
           content:
             application/problem+json:
               schema: