Widen http version constraint.

(Required for constraint solving in the SDK build.)
diff --git a/pubspec.yaml b/pubspec.yaml
index 0efb23f..4a3123e 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -9,7 +9,7 @@
 
 dependencies:
   charcode: '^1.1.0'
-  http: '^0.11.2'
+  http: '^0.11.0'
   path: '>=1.0.0 <2.0.0'
 
 dev_dependencies: