Merge pull request JedWatson#1652 from dan-diaz/isClearable

Include a className of 'is-clearable' if clearable is true

src/Select.js

@@ -1081,6 +1081,7 @@ const Select = createClass({
 		let className = classNames('Select', this.props.className, {
 			'Select--multi': this.props.multi,
 			'Select--single': !this.props.multi,
+			'is-clearable': this.props.clearable,
 			'is-disabled': this.props.disabled,
 			'is-focused': this.state.isFocused,
 			'is-loading': this.props.isLoading,