Update AceEditorWrapper.jsx (#7315)

THEN is also a keyword in SQL

superset/assets/src/SqlLab/components/AceEditorWrapper.jsx

@@ -29,7 +29,7 @@ const langTools = ace.acequire('ace/ext/language_tools');
 
 const keywords = (
   'SELECT|INSERT|UPDATE|DELETE|FROM|WHERE|AND|OR|GROUP|BY|ORDER|LIMIT|OFFSET|HAVING|AS|CASE|' +
-  'WHEN|ELSE|END|TYPE|LEFT|RIGHT|JOIN|ON|OUTER|DESC|ASC|UNION|CREATE|TABLE|PRIMARY|KEY|IF|' +
+  'WHEN|THEN|ELSE|END|TYPE|LEFT|RIGHT|JOIN|ON|OUTER|DESC|ASC|UNION|CREATE|TABLE|PRIMARY|KEY|IF|' +
   'FOREIGN|NOT|REFERENCES|DEFAULT|NULL|INNER|CROSS|NATURAL|DATABASE|DROP|GRANT|SUM|MAX|MIN|COUNT|' +
   'AVG|DISTINCT'
 );