Drop use of React.findDOMNode, fixes JedWatson#7

Author: JedWatson

src/Codemirror.js

@@ -1,6 +1,5 @@
 const React = require('react');
 const ReactDOM = require('react-dom');
-const findDOMNode = ReactDOM.findDOMNode;
 const PropTypes = require('prop-types');
 const className = require('classnames');
 const debounce = require('lodash.debounce');
@@ -44,9 +43,8 @@ const CodeMirror = createReactClass({
 		this.componentWillReceiveProps = debounce(this.componentWillReceiveProps, 0);
 	},
 	componentDidMount () {
-		const textareaNode = findDOMNode(this.refs.textarea);
 		const codeMirrorInstance = this.getCodeMirrorInstance();
-		this.codeMirror = codeMirrorInstance.fromTextArea(textareaNode, this.props.options);
+		this.codeMirror = codeMirrorInstance.fromTextArea(this.textareaNode, this.props.options);
 		this.codeMirror.on('change', this.codemirrorValueChanged);
 		this.codeMirror.on('cursorActivity', this.cursorActivity);
 		this.codeMirror.on('focus', this.focusChanged.bind(this, true));
@@ -118,7 +116,7 @@ const CodeMirror = createReactClass({
 		return (
 			<div className={editorClassName}>
 				<textarea
-					ref="textarea"
+					ref={ref => this.textareaNode = ref}
 					name={this.props.path}
 					defaultValue={this.props.value}
 					autoComplete="off"