Increase the pubspec version (#30)

I meant to do this in the last PR.
diff --git a/pubspec.yaml b/pubspec.yaml
index a537788..ec526bf 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: pub_semver
-version: 1.4.0
+version: 1.4.1
 author: Dart Team <misc@dartlang.org>
 description: >
  Versions and version constraints implementing pub's versioning policy. This