UnhandledPromiseRejectionWarning when building
I'm getting this when building with node 8.7.0:

>(node:68828) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): TypeError: c.close is not a function
>(node:68828) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

