Update options.html.markdown
Update options.html.markdown

Add example for specifying an IPv6 address.

See: https://github.com/hashicorp/serf/issues/315
samaitra/serf,mapuri/serf,pmenglund/serf,hashicorp/serf,pmenglund/serf,minhkiller/serf,hashicorp/serf,gnawhleinad/serf,mapuri/serf,hashicorp/serf,mapuri/serf,patrickviet/serf,mapuri/serf,minhkiller/serf,samaitra/serf,samaitra/serf,samaitra/serf,patrickviet/serf,mapuri/serf,pmenglund/serf,patrickviet/serf,patrickviet/serf,samaitra/serf,gnawhleinad/serf,pmenglund/serf,gnawhleinad/serf,hashicorp/serf,pmenglund/serf,gnawhleinad/serf,minhkiller/serf,mapuri/serf,patrickviet/serf,samaitra/serf,pmenglund/serf,gnawhleinad/serf,gnawhleinad/serf,hashicorp/serf,minhkiller/serf,patrickviet/serf,minhkiller/serf,minhkiller/serf