Fixes the following exception:
```
Debug: internal, implementation, error
    TypeError: Cannot read property 'Fn::Join' of undefined
    at /Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/utils/resolveJoins.js:17:28
    at Array.forEach (<anonymous>)
    at resolveJoins (/Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/utils/resolveJoins.js:15:28)
    at new LambdaFunction (/Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/lambda/LambdaFunction.js:154:56)
    at LambdaFunctionPool.get (/Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/lambda/LambdaFunctionPool.js:93:24)
    at Lambda.get (/Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/lambda/Lambda.js:60:88)
    at hapiHandler (/Users/alexhayton/personal/stablemaster/lambda/node_modules/serverless-offline/dist/events/http/HttpServer.js:511:82)
    at module.exports.internals.Manager.execute (/Users/alexhayton/personal/stablemaster/lambda/node_modules/@hapi/hapi/lib/toolkit.js:41:33)
    at Object.internals.handler (/Users/alexhayton/personal/stablemaster/lambda/node_modules/@hapi/hapi/lib/handler.js:46:48)
    at exports.execute (/Users/alexhayton/personal/stablemaster/lambda/node_modules/@hapi/hapi/lib/handler.js:31:36)
    at Request._lifecycle (/Users/alexhayton/personal/stablemaster/lambda/node_modules/@hapi/hapi/lib/request.js:312:68)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)
    at Request._execute (/Users/alexhayton/personal/stablemaster/lambda/node_modules/@hapi/hapi/lib/request.js:221:9)
```