SoftwareSerial include in NexUpload.cpp

[tomtobback]

I'm working with a SAMD board and the library does not compile because it tries to include SoftwareSerial.h in https://github.com/jyberg/Enhanced-Nextion-Library/blob/master/NexUpload.cpp even if USE_SOFTWARE_SERIAL is undefined. Please move that line into the #ifdef USE_SOFTWARE_SERIAL block, same as in https://github.com/jyberg/Enhanced-Nextion-Library/blob/master/NexHardware.cpp
With this change, the library compiles for my board.

[jyberg]

Change done