Fix support for Python 3.7 host version

Author: joerick

cibuildwheel/util.py

@@ -711,7 +711,6 @@ def parse_key_value_string(
 
     shlexer = shlex.shlex(key_value_string, posix=True, punctuation_chars=";:")
     shlexer.commenters = ""
-    shlexer.whitespace_split = True
     parts = list(shlexer)
     # parts now looks like
     # ['docker', ';', 'create_args',':', '--some-option=value', 'another-option']