Increment version number.
diff --git a/pubspec.yaml b/pubspec.yaml
index 3f50916..9c96059 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: webdriver
-version: 0.10.0-pre.3
+version: 0.10.0-pre.4
 author: Google, Inc.
 description: >
   Provides WebDriver bindings for Dart. These use the WebDriver JSON interface,