Drop the author field from pubspec (#350)

This field is no longer used by pub.
diff --git a/pubspec.yaml b/pubspec.yaml
index fa497de..57e6374 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,5 @@
 name: http
 version: 0.12.0+3
-author: "Dart Team <misc@dartlang.org>"
 homepage: https://github.com/dart-lang/http
 description: A composable, multi-platform, Future-based API for HTTP requests.