Change to encodestring to b64encode to avoid newlines in the data URI

The point of this is to improve compatibility with older browsers.
also, encodestring is depricated in python 3.

IPython/lib/display.py

@@ -138,7 +138,9 b' class Audio(DisplayObject):'
     def src_attr(self):
         import base64
         if self.embed and (self.data is not None):
-                return """data:{type};base64,{base64}""".format(type=self.mimetype, base64=base64.encodestring(self.data))
+            data = base64=base64.b64encode(self.data).decode('ascii'))
+            return """data:{type};base64,{base64}""".format(type=self.mimetype,
+                                                            base64=data)
         elif self.url is not None:
             return self.url
         else: