make initial widget size of vega to be auto (node-red#77)

node-red-node-ui-vega/ui_vega.html

@@ -60,7 +60,7 @@
  $("#node-input-size").toggleClass("input-error",!valid);
  return valid;
  }},
- height: {value: 5},
+ height: {value: 0},
  vega: {value: null}
  },
  inputs: 1,