Added a condition that adds the SoftwareSerial library for the ESP8266.

Author: daftfox

utility/SerialFirmata.h

@@ -26,7 +26,7 @@
 // SoftwareSerial is currently only supported for AVR-based boards and the Arduino 101.
 // Limited to Arduino 1.6.6 or higher because Arduino builder cannot find SoftwareSerial
 // prior to this release.
-#if (ARDUINO > 10605) && (defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_ARCH_ARC32))
+#if (ARDUINO > 10605) && (defined(ARDUINO_ARCH_AVR) || defined(ARDUINO_ARCH_ARC32) || defined(ESP8266))
 #include <SoftwareSerial.h>
 #endif