Fixed PUT(String) method, it called POST in error

About the simplest change possible, just delete two characters and add one. The PUT(String) convenience method called the full POST method instead of calling the PUT method

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -349,7 +349,7 @@ int HTTPClient::PUT(uint8_t * payload, size_t size) {
 }
 
 int HTTPClient::PUT(String payload) {
-    return POST((uint8_t *) payload.c_str(), payload.length());
+    return PUT((uint8_t *) payload.c_str(), payload.length());
 }
 
 /**