does jetcd support ipv6 cluster ip?

**Versions**
- jetcd: 0.7.7
- java: 1.8
the code is
```
List endpoints = Arrays.asList(
URI.create("http://[2001:db8::1]:2379"),
URI.create("http://[2001:db8::2]:2379")
);
Client client = Client.builder().endpoints(endpoints).build();
KV kvClient = client.getKVClient();
```
exception is
```
Exception in thread "main" java.lang.IllegalArgumentException: cannot find a NameResolver for ip:///[2001:db8::1]:2379,[2001:db8::2]:2379 (Illegal character in path at index 6: ip:///[2001:db8::1]:2379,[2001:db8::2]:2379)
at io.grpc.internal.ManagedChannelImpl.getNameResolver(ManagedChannelImpl.java:773)
at io.grpc.internal.ManagedChannelImpl.getNameResolver(ManagedChannelImpl.java:782)
at io.grpc.internal.ManagedChannelImpl.(ManagedChannelImpl.java:662)
at io.grpc.internal.ManagedChannelImplBuilder.build(ManagedChannelImplBuilder.java:631)
at io.grpc.internal.AbstractManagedChannelImplBuilder.build(AbstractManagedChannelImplBuilder.java:297)
at io.vertx.grpc.VertxChannelBuilder.build(VertxChannelBuilder.java:309)
at io.etcd.jetcd.impl.ClientConnectionManager.getChannel(ClientConnectionManager.java:70)
at io.etcd.jetcd.impl.ClientConnectionManager.newStub(ClientConnectionManager.java:102)
at io.etcd.jetcd.impl.KVImpl.(KVImpl.java:51)
at io.etcd.jetcd.impl.ClientImpl.lambda$new$0(ClientImpl.java:48)
at io.etcd.jetcd.support.MemorizingClientSupplier.get(MemorizingClientSupplier.java:37)
at io.etcd.jetcd.impl.ClientImpl.getKVClient(ClientImpl.java:65)
```