empty input value so that same file can be selected multiple times

fixes #531

src/plugins/Dashboard/ActionBrowseTagline.js

@@ -27,6 +27,7 @@ class ActionBrowseTagline extends Component {
           name="files[]"
           multiple="true"
           onchange={this.props.handleInputChange}
+          value=""
           ref={(input) => {
             this.input = input
           }} />

src/plugins/Dashboard/Tabs.js

@@ -48,6 +48,7 @@ class Tabs extends Component {
             name="files[]"
             multiple="true"
             onchange={this.props.handleInputChange}
+            value=""
             ref={(input) => { this.input = input }} />
         </li>
         {this.props.acquirers.map((target) => {