update ReactNative to React Native (fixes vuejs#717)

Author: chrisvfritz

src/v2/guide/comparison.md

@@ -221,9 +221,9 @@ Since you don't need to know about JSX, ES2015, or build systems to get started
 
 ### Native Rendering
 
-ReactNative enables you to write native-rendered apps for iOS and Android using the same React component model. This is great in that as a developer, you can apply your knowledge of a framework across multiple platforms. On this front, Vue has an official collaboration with [Weex](https://alibaba.github.io/weex/), a cross-platform UI framework developed by Alibaba Group, which uses Vue as its JavaScript framework runtime. This means with Weex, you can use the same Vue component syntax to author components that can not only be rendered in the Browser, but also natively on iOS and Android!
+React Native enables you to write native-rendered apps for iOS and Android using the same React component model. This is great in that as a developer, you can apply your knowledge of a framework across multiple platforms. On this front, Vue has an official collaboration with [Weex](https://alibaba.github.io/weex/), a cross-platform UI framework developed by Alibaba Group, which uses Vue as its JavaScript framework runtime. This means with Weex, you can use the same Vue component syntax to author components that can not only be rendered in the Browser, but also natively on iOS and Android!
 
-At this moment, Weex is still in active development and is not as mature and battle-tested as ReactNative, but its development is driven by the production needs of the largest e-commerce business in the world, and the Vue team will also actively collaborate with the Weex team to ensure a smooth experience for Vue developers.
+At this moment, Weex is still in active development and is not as mature and battle-tested as React Native, but its development is driven by the production needs of the largest e-commerce business in the world, and the Vue team will also actively collaborate with the Weex team to ensure a smooth experience for Vue developers.
 
 ### With MobX