Summary:
When trying to build in the latest beta version of unity, the build will fail with the following message:

\Assets/GoogleVR/Editor/GvrBuildProcessor.cs(29,7): error CS0535: 'GvrBuildProcessor' does not implement interface member 'UnityEditor.Build.IPreprocessBuild.OnPreprocessBuild(UnityEditor.Build.Reporting.BuildReport)'

Found using:

• Google VR SDK version: 1.120.0
• Unity version: 2018.1.0b9
• Phone manufacturer, model, and O/S version: any iOS
• Viewer manufacturer & model: N/A

Steps to reproduce the issue:

1. Start unity
2. Import HelloVr scene.
3. Configure as per ios quickstart documentation
4. Build

Workarounds:
Don't use a beta release.

Additional comments: