Fix bin process not always exiting

[jogold]

What did you implement:

Closes #5348

How did you implement it:

Add .then(() => process.exit(0)) after serverless.run() in bin file.

Todos:

• Fix linting errors
• Make sure code coverage hasn't dropped
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[horike37]

@jogold
Good point. Agreed with the approach.
LGTM 👍

[brunotag]

FYI this is now breaking the serverless-alexa-skills plugin, see marcy-terui/serverless-alexa-skills#24

[bradbenvenuti]

This also seems to be breaking sls invoke local for nodejs when using callbacks.

For example - when running this handler function with sls invoke local, the cli exits before the callback is run:

module.exports.hello = (event, context, callback) => {
    setTimeout(function(err, obj) {
        callback({
            statusCode: 200,
            body: JSON.stringify({
                message: 'Go Serverless v1.0! Your function executed successfully!',
                input: event
            })
        })
    }, 1000);
};