Fix typo

Apparently typeof is required in the PluginFunction signature
pagekit · steffans · Feb 11, 2018 · May 26, 2017 · May 26, 2017 · Jun 2, 2017
commit fdbf30b43f887d2be3445c37c57b007e0439edb0
diff --git a/types/index.d.ts b/types/index.d.ts
@@ -91,4 +91,4 @@ export interface Resource extends $resource {
     actions: ResourceActions;
 }
 
-export declare function install(vue: _Vue): void;
+export declare function install(vue: typeof _Vue): void;