[mapbox] fix viewport alterations (#3293)

* [mapbox] fix viewport alterations

Since explorev2 it appears that altering the viewport hasn't been
changing the controls as it used to. This PR addresses it.

* lint

superset/assets/javascripts/explore/components/controls/TextControl.jsx

@@ -29,13 +29,10 @@ const defaultProps = {
 export default class TextControl extends React.Component {
   constructor(props) {
     super(props);
-    const value = props.value ? props.value.toString() : '';
-    this.state = { value };
     this.onChange = this.onChange.bind(this);
   }
   onChange(event) {
     let value = event.target.value || '';
-    this.setState({ value });
 
     // Validation & casting
     const errors = [];
@@ -58,6 +55,7 @@ export default class TextControl extends React.Component {
     this.props.onChange(value, errors);
   }
   render() {
+    const value = this.props.value ? this.props.value.toString() : '';
     return (
       <div>
         <ControlHeader {...this.props} />
@@ -66,7 +64,7 @@ export default class TextControl extends React.Component {
             type="text"
             placeholder=""
             onChange={this.onChange}
-            value={this.state.value}
+            value={value}
           />
         </FormGroup>
       </div>