Remove the "Filing Bugs" section of the README. (#80)

Most packages don't have this section, and it's pretty clear that users
are supposed to file issues on GitHub.
diff --git a/README.md b/README.md
index 506bbad..8d85291 100644
--- a/README.md
+++ b/README.md
@@ -91,10 +91,3 @@
   print('Response body: ${response.body}');
 }
 ```
-
-## Filing issues
-
-Please file issues for the http package at [http://dartbug.com/new][bugs].
-
-[bugs]: http://dartbug.com/new
-[docs]: https://api.dartlang.org/docs/channels/dev/latest/http.html