Update string-transformations.md

Fixing the sample code

Author: yoelhor

articles/active-directory-b2c/string-transformations.md

@@ -670,7 +670,7 @@ Checks whether the provided email address is valid, and return the email alias.
 - Input claims:
     - **claimToMatch**: "[email protected]"
 - Input parameters:
-    - **matchTo**: "(?<mailAlias>.*)@(.*)$"
+    - **matchTo**: `(?<mailAlias>.*)@(.*)$`
     - **outputClaimIfMatched**:  "isEmail"
     - **extractGroups**: true
 - Output claims: