message: refactor: improve error msg for non-reactive properties
  close
diff: @@ -16,8 +16,10 @@ if (process.env.NODE_ENV !== 'production') {
  const warnNonPresent = (target, key) => {
  warn(
  `Property or method "${key}" is not defined on the instance but` +
  - `referenced during render. Make sure to declare reactive data ` +
  - `properties in the data option.`,
  + 'referenced during render. Make sure that this property is reactive, ' +
  + 'either in the data option, or for class-based components, by ' +
  + 'initializing the property.' +
  + 'See: https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties.',
  target
  )
  }
  