Currently, AppBuilder does not support NativeScript 3.0 RC. The error that you are experiencing is due to the fact that the AppBuilder servers and the NativeScript 3.0 RC are using different versions of TypeScript. Unfortunately, there is no workaround that will help you to resolve this issue.
Having said that, we plan to introduce support for NativeScript 3.0 as soon as they announce a final, stable version.
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