Not compatible with Windows

[triqi]

Issue

Using this library under Windows (cmd) does not spawn the DynamoDB java process.

Possible solution

1. Passing in the shell: true option into child_process.spawn would execute the command in a shell.
2. Replace child_process.spawn with a cross platform compatible shell library such as shelljs.

[MikhailSemichev]

Doesn't work on windows as well. sls offline start fails

[stefancruz]

It seems to work fine in powershell.

[RyanFelt]

I am running this fine on windows, all I had to do was pass in a callback function to install.
dynamodbLocal.install( () => {} );

[stefancruz]

dynamodbLocal.install( () => {} );

I did a pull request to update the documentation regarding this issue, but it still open.

#36