update pubsubclient release to 2.7

lib/pubsubclient/README.md

@@ -8,7 +8,7 @@ a server that supports MQTT.
 The library comes with a number of example sketches. See File > Examples > PubSubClient
 within the Arduino application.
 
-Full API documentation is available here: http://pubsubclient.knolleary.net
+Full API documentation is available here: https://pubsubclient.knolleary.net
 
 ## Limitations
 
@@ -37,6 +37,7 @@ boards and shields, including:
  - TI CC3000 WiFi - [library](https://github.com/sparkfun/SFE_CC3000_Library)
  - Intel Galileo/Edison
  - ESP8266
+ - ESP32
 
 The library cannot currently be used with hardware based on the ENC28J60 chip –
 such as the Nanode or the Nuelectronics Ethernet Shield. For those, there is an