Change fromString constructor to parse static method

pkg/http/lib/src/response.dart

Index: pkg/http/lib/src/response.dart
diff --git a/pkg/http/lib/src/response.dart b/pkg/http/lib/src/response.dart
index c036fe91b8b0d44f689575e13fd8b83fb1b65ad5..b7e0a481da810db6a4884f9e974a727fb5b0a41e 100644
--- a/pkg/http/lib/src/response.dart
+++ b/pkg/http/lib/src/response.dart
@@ -89,6 +89,6 @@ Encoding _encodingForHeaders(Map<String, String> headers) =>
 /// `application/octet-stream`.
 ContentType _contentTypeForHeaders(Map<String, String> headers) {
   var contentType = headers[HttpHeaders.CONTENT_TYPE];
-  if (contentType != null) return new ContentType.fromString(contentType);
+  if (contentType != null) return ContentType.parse(contentType);
   return new ContentType("application", "octet-stream");
 }