[e2e] Bump version to 0.6.0 (flutter#2855)

Missed this earlier in flutter#2854

Author: jiahaog

packages/e2e/pubspec.yaml

@@ -1,6 +1,6 @@
 name: e2e
 description: Runs tests that use the flutter_test API as integration tests.
-version: 0.5.0+1
+version: 0.6.0
 homepage: https://github.com/flutter/plugins/tree/master/packages/e2e
 
 environment: