Fixed TypeError when a unicode generator name was passed on Python 2.7

Fixes #388.

Author: agronholm

docs/news.rst

@@ -1,6 +1,12 @@
 Release Notes
 =============
 
+**UNRELEASED**
+
+- Fixed regression introduced in 0.36.0 on Python 2.7 when a custom generator
+  name was passed as unicode (Scikit-build)
+  (``TypeError: 'unicode' does not have the buffer interface``)
+
 **0.36.0 (2020-12-01)**
 
 - Added official Python 3.9 support

src/wheel/bdist_wheel.py

@@ -373,6 +373,11 @@ def run(self):
 
     def write_wheelfile(self, wheelfile_base, generator='bdist_wheel (' + wheel_version + ')'):
         from email.message import Message
+
+        # Workaround for Python 2.7 for when "generator" is unicode
+        if sys.version_info < (3,) and not isinstance(generator, str):
+            generator = generator.encode('utf-8')
+
         msg = Message()
         msg['Wheel-Version'] = '1.0'  # of the spec
         msg['Generator'] = generator