Ttl Heartbeats don't send acl token if configured

If heartbeat is enabled paired with acl tokens, then the heartbeat task does not configure the token to use when communicating with the consul server

spring.cloud.consul.discovery:
  acl-token: ${uuid}
  heartbeat.enabled: true

ConsulHeartbeatTask has this method call to agentCheckPass:

@Override
public void run() {
	TtlScheduler.this.client.agentCheckPass(this.checkId);
	if (log.isDebugEnabled()) {
		log.debug("Sending consul heartbeat for: " + this.checkId);
	}
}

Which without a token, you'll see the following stack trace:

com.ecwid.consul.v1.OperationException: OperationException(statusCode=403, statusMessage='Forbidden', statusContent='Permission denied')
        at com.ecwid.consul.v1.agent.AgentConsulClient.agentCheckPass(AgentConsulClient.java:211) ~[consul-api-1.4.1.jar:na]
        at com.ecwid.consul.v1.agent.AgentConsulClient.agentCheckPass(AgentConsulClient.java:198) ~[consul-api-1.4.1.jar:na]
        at com.ecwid.consul.v1.agent.AgentConsulClient.agentCheckPass(AgentConsulClient.java:193) ~[consul-api-1.4.1.jar:na]
        at com.ecwid.consul.v1.ConsulClient.agentCheckPass(ConsulClient.java:259) ~[consul-api-1.4.1.jar:na]
        at org.springframework.cloud.consul.discovery.TtlScheduler$ConsulHeartbeatTask.run(TtlScheduler.java:95) ~[spring-cloud-consul-discovery-2.1.1.RELEASE.jar:2.1.1.RELEASE]

Which can be overridden to pass a token too (can be null too):

@Override
public void run() {
	TtlScheduler.this.client.agentCheckPass(this.checkId, this.aclToken);
	if (log.isDebugEnabled()) {
		log.debug("Sending consul heartbeat for: " + this.checkId);
	}
}

So any reason why i can't submit a simple PR to fix this (Ie am i missing something?)

Start with TtlScheduler.java and the ConsulHeartbeatTask.run entry point shown in the issue, then inspect how the ACL token is configured for the heartbeat. Done means TTL heartbeats pass the configured token to Consul, while still allowing a null token.