fix warning in checbox in form field.

client/src/core-components/form-field.js

@@ -195,7 +195,11 @@ class FormField extends React.Component {
             props.values = value;
         }
 
-        props.value = value;
+        if(field === 'checkbox') {
+            props.value = !!value;
+        } else {
+            props.value = value;
+        }
 
         return props;
     }