0.2.19 -> 0.2.20 breaks serverless offline start

Upgrading from 0.2.19 to 0.2.20 and any later release breaks the command

`serverless offline start`

`serverless offline` still works.

I'm using serverless-webpack

```
plugins:
- serverless-webpack
- serverless-dynamodb-local
- serverless-offline
```

and versions are:
sls-offline: 3.15.3
serverless-webpack: 2.2.2 and I've tried other versions with same result.
serverless: 1.20.2

I don't see the release tags in this repo unfortunately. Also, the error is a bit unspecific:
```
SLS_DEBUG=* node_modules/.bin/serverless offline start
Serverless: WARNING: Plugin ServerlessWebpack uses deprecated hook before:deploy:createDeploymentArtifacts,
use package:createDeploymentArtifacts hook instead
Serverless: WARNING: Plugin ServerlessWebpack uses deprecated hook after:deploy:createDeploymentArtifacts,
use package:createDeploymentArtifacts hook instead
Serverless: Bundling with Webpack...
Time: 2423ms
Asset Size Chunks Chunk Names
handler.js 222 kB 0 [emitted] main
Serverless: Watching with Webpack...
events.js:160
throw er; // Unhandled 'error' event
^

Error: spawn java ENOENT
at exports._errnoException (util.js:1018:11)
at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
at onErrorNT (internal/child_process.js:367:16)
at _combinedTickCallback (internal/process/next_tick.js:80:11)
at process._tickDomainCallback (internal/process/next_tick.js:128:9)
```

Start by reproducing `serverless offline start` with the listed plugin and version combinations, then compare it with `serverless offline`. Trace the serverless-dynamodb-local startup path around the `spawn java ENOENT` error; done means the start command works without the unhandled error while preserving the existing offline command.

Written by the indexing model from the issue text.