fix: check reflectionIsSupported in decorator runtime (#350)

* check reflectionIsSupported in decorator runtime

* fix lint

Author: vitalishapovalov

Diff for: src/component.ts

@@ -83,7 +83,7 @@ export function componentFactory (
 
   forwardStaticMembers(Extended, Component, Super)
 
-  if (reflectionIsSupported) {
+  if (reflectionIsSupported()) {
     copyReflectionMetadata(Extended, Component)
   }
 

Diff for: src/reflect.ts

@@ -4,7 +4,9 @@ import { VueClass } from './declarations'
 // The rational behind the verbose Reflect-feature check below is the fact that there are polyfills
 // which add an implementation for Reflect.defineMetadata but not for Reflect.getOwnMetadataKeys.
 // Without this check consumers will encounter hard to track down runtime errors.
-export const reflectionIsSupported = typeof Reflect !== 'undefined' && Reflect.defineMetadata && Reflect.getOwnMetadataKeys
+export function reflectionIsSupported () {
+  return typeof Reflect !== 'undefined' && Reflect.defineMetadata && Reflect.getOwnMetadataKeys
+}
 
 export function copyReflectionMetadata (
   to: VueConstructor,