Update changelog format (#41)

CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 80c0078..dec400e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,11 +1,9 @@
 ## 2.1.6
-
-- Cast stream to List<int> in 'readAsString', this is in preparation for
-  HttpClientResponse implementing Stream<Uint8List> (forward compatible
+- Cast stream to `List<int>` in 'readAsString', this is in preparation for
+  `HttpClientResponse` implementing `Stream<Uint8List>` (forward compatible
   change, should be a no-op for existing usages)
 
 ## 2.1.5
-
 - Require at least Dart 2.0.0-dev.61.
 
 ## 2.1.4