Make dump() work Python 3.3
diff --git a/jinja2/environment.py b/jinja2/environment.py
index ed59779..58573a2 100644
--- a/jinja2/environment.py
+++ b/jinja2/environment.py
@@ -1069,7 +1069,7 @@
         """
         close = False
         if isinstance(fp, six.string_types):
-            fp = open(fp, 'w')
+            fp = open(fp, encoding is None and 'w' or 'wb')
             close = True
         try:
             if encoding is not None: