Bump version

This publishes strong mode fixes.

Are there any further steps beyond tagging and pub lish?

R=jmesserly@google.com

Review URL: https://codereview.chromium.org//1626593002 .
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 665d668..690c9a0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+#### 0.13.4
+
+* Fixed strong mode errors and warnings
+
 #### 0.13.3+1
 
 * Add support for code_transformers `0.4.x`.
diff --git a/pubspec.yaml b/pubspec.yaml
index 845068f..84dca81 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: observe
-version: 0.13.3+1
+version: 0.13.4
 author: Polymer.dart Authors <web-ui-dev@dartlang.org>
 description: >
   Observable properties and objects for use in template_binding.