Keep mimetypes as str on all versions of Python.

As noted in jazzband#297 the mimetypes should not be
`unicode` *on Python 2*. But they should be `str` on Python 3.

Caused by: jazzband#297
Effecting:
- pallets/werkzeug#636
- pallets/werkzeug#637

AUTHORS

@@ -21,6 +21,7 @@ or just made Pipeline more awesome.
  * Austin Pua <[email protected]>
  * Axel Haustant <[email protected]>
  * Balazs Kossovics <[email protected]>
+ * Ben Spaulding <[email protected]>
  * Ben Vinegar <[email protected]>
  * Brad Pitcher <[email protected]>
  * Brant Young <[email protected]>

docs/configuration.rst

@@ -231,11 +231,11 @@ Tuple that match file extension with their corresponding mimetypes.
 Defaults to ::
 
   (
-    (b'text/coffeescript', '.coffee'),
-    (b'text/less', '.less'),
-    (b'text/javascript', '.js'),
-    (b'text/x-sass', '.sass'),
-    (b'text/x-scss', '.scss')
+    ('text/coffeescript', '.coffee'),
+    ('text/less', '.less'),
+    ('text/javascript', '.js'),
+    ('text/x-sass', '.sass'),
+    ('text/x-scss', '.scss')
   )
 
 .. warning::

pipeline/conf.py

@@ -71,11 +71,11 @@
     'LESS_ARGUMENTS': '',
 
     'MIMETYPES': (
-        (b'text/coffeescript', '.coffee'),
-        (b'text/less', '.less'),
-        (b'text/javascript', '.js'),
-        (b'text/x-sass', '.sass'),
-        (b'text/x-scss', '.scss')
+        (str('text/coffeescript'), str('.coffee')),
+        (str('text/less'), str('.less')),
+        (str('text/javascript'), str('.js')),
+        (str('text/x-sass'), str('.sass')),
+        (str('text/x-scss'), str('.scss'))
     ),
 
     'EMBED_MAX_IMAGE_SIZE': 32700,

tests/tests/test_utils.py

@@ -1,3 +1,8 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+import mimetypes
+
 from django.test import TestCase
 
 from pipeline.utils import guess_type
@@ -8,3 +13,8 @@ def test_guess_type(self):
         self.assertEqual('text/css', guess_type('stylesheet.css'))
         self.assertEqual('text/coffeescript', guess_type('application.coffee'))
         self.assertEqual('text/less', guess_type('stylesheet.less'))
+
+    def test_mimetypes_are_str(self):
+        for ext, mtype in mimetypes.types_map.items():
+            self.assertIsInstance(ext, str)
+            self.assertIsInstance(mtype, str)