Specifying term_char is broken

[jorenko]

I get this traceback when specifying term_char on python 3.8:

File "/usr/lib/python3.8/site-packages/vxi11/vxi11.py", line 727, in write
self.write_raw(str(message).encode(encoding))
File "/usr/lib/python3.8/site-packages/vxi11/vxi11.py", line 640, in write_raw
data += term_char
TypeError: can't concat int to bytes

It seems this can be fixed by changing line 639 from:
term_char = str(self.term_char).encode('utf-8')[0]
to:
term_char = str(self.term_char).encode('utf-8')[:1]