Fix typo in package name (#299)

Author: robert-ancell

.github/ISSUE_TEMPLATE/3-FEATURE_REQUEST.md

@@ -13,6 +13,6 @@ about: You are using `package:http` and would like a new feature to make it
   Note that this package is designed to be cross-platform and we will only be
   able to add features which can be supported with _both_ `dart:io` and
   `dart:html`. If you're looking for a feature which is already supported by the
-  `daart:io` HttpClient constructor you can construct one manually and pass it
+  `dart:io` HttpClient constructor you can construct one manually and pass it
   to the IOClient constructor directly.
 -->