Update MIGRATION.md

Co-authored-by: Francesco Novy <[email protected]>

Author: Luca Forstner

MIGRATION.md

@@ -316,7 +316,7 @@ hub.captureException()
 
 instead capture isolated events as follows:
 
-````
+```js
 // NEW
 const client = new Client();
 const scope = new Scope();