Fix python 3.8 regression on macOS

Author: michael-lazar

rtv/terminal.py

@@ -14,6 +14,7 @@
 import subprocess
 import curses.ascii
 from curses import textpad
+import multiprocessing
 from multiprocessing import Process
 from contextlib import contextmanager
 from tempfile import NamedTemporaryFile
@@ -42,6 +43,9 @@
 
 _logger = logging.getLogger(__name__)
 
+# https://stackoverflow.com/a/72830812
+multiprocessing.set_start_method("fork")
+
 
 class Terminal(object):