docs(README): add syntax highlight for code

Author: probil

README.md

@@ -3,12 +3,12 @@ A small wrapper for integrating axios to Vuejs
 
 ## How to install:
 ### CommonJS:
-```
+```bash
 npm install --save axios vue-axios
 ```
 
 And in your entry file:
-```
+```js
 import Vue from 'vue'
 import axios from 'axios'
 import VueAxios from 'vue-axios'
@@ -23,7 +23,7 @@ Just add 3 scripts in order: `vue`, `axios` and `vue-axios` to your `document`.
 This wrapper bind `axios` to `Vue` or `this` if you're using single file component.
 
 You can `axios` like this:
-```
+```js
 Vue.axios.get(api).then((response) => {
   console.log(response.data)
 })