Fixing monitor prop type warning for scalar variable monitors.

src/components/monitor/monitor.jsx

@@ -42,7 +42,9 @@ MonitorComponent.propTypes = {
     componentRef: PropTypes.func.isRequired,
     label: PropTypes.string.isRequired,
     onDragEnd: PropTypes.func.isRequired,
-    value: PropTypes.string.isRequired
+    value: PropTypes.oneOfType([
+        PropTypes.string,
+        PropTypes.number])
 };
 
 MonitorComponent.defaultProps = {