message: update requirements esp8266 2.4.0
diff: @@ -77,7 +77,7 @@ First attempt at a library. Lots more changes and fixes to do. Contributions are
  You can either install through the Arduino Library Manager or checkout the latest changes or a release from github
  #### Install through Library Manager
  -__Currently version 0.8+ works with release 2.0.0 or newer of the [ESP8266 core for Arduino](https://github.com/esp8266/Arduino)__
  +__Currently version 0.8+ works with release 2.4.0 or newer of the [ESP8266 core for Arduino](https://github.com/esp8266/Arduino)__
  - in Arduino IDE got to Sketch/Include Library/Manage Libraries
  ![Manage Libraries](http://i.imgur.com/9BkEBkR.png)
  @@ -87,7 +87,7 @@ __Currently version 0.8+ works with release 2.0.0 or newer of the [ESP8266 core
  - click Install and start [using it](#using)
  #### Checkout from github
  -__Github version works with release 2.0.0 or newer of the [ESP8266 core for Arduino](https://github.com/esp8266/Arduino)__
  +__Github version works with release 2.4.0 or newer of the [ESP8266 core for Arduino](https://github.com/esp8266/Arduino)__
  - Checkout library to your Arduino libraries folder
  ### Using
  