Fix(types): inject() return type

use undefined as return type instead of void

close #290

Author: LinusBorg

src/apis/inject.ts

@@ -32,9 +32,9 @@ export function provide<T>(key: InjectionKey<T> | string, value: T): void {
   vm._provided[key as string] = value;
 }
 
-export function inject<T>(key: InjectionKey<T> | string): T | void;
+export function inject<T>(key: InjectionKey<T> | string): T | undefined;
 export function inject<T>(key: InjectionKey<T> | string, defaultValue: T): T;
-export function inject<T>(key: InjectionKey<T> | string, defaultValue?: T): T | void {
+export function inject<T>(key: InjectionKey<T> | string, defaultValue?: T): T | undefined {
   if (!key) {
     return defaultValue;
   }