fix(delete-button.jsx): onClick may be a boolean (#160)

Expected onClick listener to be a function, instead got a value of boolean type.

Author: behzad888

Diff for: package.json

@@ -1,6 +1,6 @@
 {
   "name": "react-fine-uploader",
-  "version": "1.0.8",
+  "version": "1.0.9",
   "license": "MIT",
   "description": "React UI components for using Fine Uploader in a React-based project.",
   "author":     {

Diff for: src/delete-button.jsx

@@ -65,7 +65,7 @@ class DeleteButton extends Component {
                 <button aria-label='delete'
                         className={ `react-fine-uploader-delete-button ${this.props.className || ''}` }
                         disabled={ !this.state.deletable || this.state.deleting }
-                        onClick={ this.state.deletable && !this.state.deleting && this._onClick }
+                        onClick={ (this.state.deletable && !this.state.deleting) ? this._onClick : null }
                         type='button'
                         { ...elementProps }
                 >