Fix piping script into docker bash

cibuildwheel/linux.py

@@ -69,7 +69,10 @@ def build(project_dir, output_dir, test_command, test_requires, test_extras, bef
                     constraints_file = dependency_constraints.get_for_python_version(config.version)
                     subprocess.run(['docker', 'cp', os.path.abspath(constraints_file), container_name + ':/constraints.txt'])
 
-                subprocess.run(['docker', 'start', '-i', '-a', container_name], stdin_str='''
+                subprocess.run(
+                    ['docker', 'start', '-i', '-a', container_name],
+                    universal_newlines=True,
+                    input='''
                         set -o errexit
                         set -o xtrace
                         mkdir -p /output
@@ -172,7 +175,8 @@ def build(project_dir, output_dir, test_command, test_requires, test_extras, bef
                         uid=os.getuid(),
                         gid=os.getgid(),
                         dependency_install_flags='-c /constraints.txt' if dependency_constraints else '',
-                ))
+                    )
+                )
 
             # copy the output back into the host
             subprocess.run(['docker', 'cp', container_name + ':/output/.', os.path.abspath(output_dir)])