Specify utf-8 encoding explicitly in tests

If we don't specify it, smart_open will use the system encoding.  This
may be ascii on some systems (e.g. Py2.7), which will fail the test
because it contains non-ascii characters.

smart_open/tests/test_smart_open.py

@@ -977,12 +977,15 @@ def test_r(self):
         text = u"физкульт-привет!"
         key.set_contents_from_string(text.encode("utf-8"))
 
-        with smart_open.s3_open_key(key, "r") as fin:
-            self.assertEqual(fin.read(), u"физкульт-привет!")
+        with smart_open.s3_open_key(key, "rb") as fin:
+            self.assertEqual(fin.read(), text.encode('utf-8'))
+
+        with smart_open.s3_open_key(key, "r", encoding='utf-8') as fin:
+            self.assertEqual(fin.read(), text)
 
         parsed_uri = smart_open.ParseUri("s3://bucket/key")
-        with smart_open.s3_open_uri(parsed_uri, "r") as fin:
-            self.assertEqual(fin.read(), u"физкульт-привет!")
+        with smart_open.s3_open_uri(parsed_uri, "r", encoding='utf-8') as fin:
+            self.assertEqual(fin.read(), text)
 
     def test_bad_mode(self):
         """Bad mode should raise and exception."""