Use latest pip on macos

cibuildwheel/macos.py

@@ -18,6 +18,8 @@ def build(project_dir, package_name, output_dir, test_command, test_requires, be
         PythonConfiguration(version='3.5', identifier='cp35-macosx_10_6_intel', url='https://www.python.org/ftp/python/3.5.4/python-3.5.4-macosx10.6.pkg'),
         PythonConfiguration(version='3.6', identifier='cp36-macosx_10_6_intel', url='https://www.python.org/ftp/python/3.6.5/python-3.6.5-macosx10.6.pkg'),
     ]
+    get_pip_url = 'https://bootstrap.pypa.io/get-pip.py'
+    get_pip_script = '/tmp/get-pip.py'
 
     pkgs_output = subprocess.check_output(['pkgutil',  '--pkgs'])
     if sys.version_info[0] >= 3:
@@ -35,6 +37,9 @@ def build(project_dir, package_name, output_dir, test_command, test_requires, be
 
     abs_project_dir = os.path.abspath(project_dir)
 
+    # get latest pip once and for all
+    call(['curl', '-L', '-o', get_pip_script, get_pip_url])
+
     for config in python_configurations:
         if skip(config.identifier):
             print('cibuildwheel: Skipping build %s' % config.identifier, file=sys.stderr)
@@ -63,7 +68,7 @@ def build(project_dir, package_name, output_dir, test_command, test_requires, be
         call([python, '--version'], env=env)
 
         # install pip & wheel
-        call([python, '-m', 'ensurepip', '--upgrade'], env=env)
+        call([python, get_pip_script, '--no-setuptools', '--no-wheel'], env=env)
         call([pip, '--version'], env=env)
         call([pip, 'install', 'wheel'], env=env)
         call([pip, 'install', 'delocate'], env=env)