refactor: fix eslint-disable directive

A few lines above we have a `eslint-disable`, so the next one should be
`eslint-enable` to reactivate Prettier.

ember-cli-build.js

@@ -50,6 +50,6 @@ module.exports = function (defaults) {
         },
       },
     },
-    /* eslint-disable prettier/prettier */
+    /* eslint-enable prettier/prettier */
   });
 };