Fix AmrDeveloper#77: Fix case expression in docs

Author: AmrDeveloper

docs/expression/case.md

@@ -1,5 +1,5 @@
 Case expression is similar to Switch Expression in many languages, it's return the value of the first branch that has condition evaluated to true, if not branch found it will return the default value
 
 ```sql
-SELECT name FROM branches WHERE (CASE WHERE isRemote THEN 1 ELSE 0 END) > 0
+SELECT name FROM branches WHERE (CASE WHEN isRemote THEN 1 ELSE 0 END) > 0
 ```