Support for lambda task

[jkucharski]

Updating the aws-sdk dependency to the latest will allow:

decisionTask.response.addDecision({
"decisionType":"ScheduleLambdaFunction",
"scheduleLambdaFunctionDecisionAttributes": {
"id": "someid",
"name": "MyLambdaFunction",
"input": "input"
}
});

This allows calling lambda functions as activities... A real nice feature.

Right now fails because the swf model in the aws-sdk does not include the newer lambda task items (ScheduleLambdaFunction,scheduleLambdaFunctionDecisionAttributes).

Clearly schedule_lambda would be a nice addition to the decision-response module as well.