Make description of activity optional (#20)

src/js/components/Form.js

@@ -22,9 +22,7 @@ class Form extends Component {
 
   isValid = () => {
     const { changeset } = this.props
-    return ["assignment_id", "task_id", "hours", "description"]
-      .map(prop => changeset[prop])
-      .every(Boolean)
+    return ["assignment_id", "task_id", "hours"].map(prop => changeset[prop]).every(Boolean)
   }
 
   handleTextareaKeyDown = event => {