updating "transpile" to "transpiling"

Author: raclim

developer_docs/development.md

@@ -87,7 +87,7 @@ Structure your commit message like this:
 
  - For common and reusable styles, write OOSCSS (Object-Oriented SCSS) with placeholders and mixins. For organizing styles, follow the [7-1 Pattern](https://sass-guidelin.es/#the-7-1-pattern) for Sass.
 
- - We're using [ES6](http://es6-features.org/) and transpile to ES5 using [Babel](https://babeljs.io/). 
+ - We're using [ES6](http://es6-features.org/) and transpiling to ES5 using [Babel](https://babeljs.io/). 
 
  - For reference to the JavaScript style guide, see the [Airbnb Style Guide](https://github.com/airbnb/javascript), [React ESLint Plugin](https://github.com/yannickcr/eslint-plugin-react).