json -> js, for syntax highlighting

src/guide/04-using-rollup-with-babel.md

@@ -26,7 +26,7 @@ export default {
 
 Before Babel will actually compile your code, it needs to be configured. Create a new file, `src/.babelrc`:
 
-```json
+``js
 {
   "presets": [
     [

src/guide/05-using-rollup-with-npm.md

@@ -8,7 +8,7 @@ First, we need a package.json file, thereunto run the command
   
  which returns the file
   
-  ```json
+  ``js
   {
     "name": "name-your-project",
     "version": "1.0.0",