refactor(shared): update genStaticKeys (vuejs#13010)

Author: mikoloism

src/shared/util.ts

@@ -286,9 +286,7 @@ export function genStaticKeys(
   modules: Array<{ staticKeys?: string[] } /* ModuleOptions */>
 ): string {
   return modules
-    .reduce((keys, m) => {
-      return keys.concat(m.staticKeys || [])
-    }, [] as string[])
+    .reduce<string[]>((keys, m) => keys.concat(m.staticKeys || []), [])
     .join(',')
 }