Allow integer env vars

[rpappalax]

when value of env var is specified as an integer, lambda function fails with error below.
ardere run succeeds when integer env var is wrapped in quotes like so:
"my_first_little_int_var": "999"

{"error":"IndexError","cause":"{\"stackTrace\": [[\"/var/task/handler.py\", 52, \"check_drain\", \"return AsynchronousPlanRunner(event, context).check_drained()\"], [\"/var/task/ardere/step_functions.py\", 365, \"check_drained\", \"if self.ecs.all_services_done(self.event[\\\"steps\\\"]):\"], [\"/var/task/ardere/aws.py\", 658, \"all_services_done\", \"return all(results)\"], [\"/var/task/concurrent/futures/_base.py\", 581, \"result_iterator\", \"yield future.result()\"], [\"/var/task/concurrent/futures/_base.py\", 398, \"result\", \"return self.__get_result()\"], [\"/var/task/concurrent/futures/thread.py\", 55, \"run\", \"result = self.fn(*self.args, **self.kwargs)\"], [\"/var/task/ardere/aws.py\", 649, \"service_done\", \"service = response[\\\"services\\\"][0]\"]], \"errorType\": \"IndexError\", \"errorMessage\": \"list index out of range\"}"}