Fix regex to parse endpoint in url with 2 letter country suffix

[adhulipa]

I modfied the regex to exclude the match from the top level domain

I tested it out on https://regex101.com/ with the following input:

1. some-cluster-identifier.cn-northwest-1.es.amazonaws.com.cn
2. some-cluster-identifier.us-west-2.es.amazonaws.com

Earlier, the region in url 1. was not being parsed correctly

[adhulipa]

https://github.com/santthosh/aws-es-kibana/issues/46

[santthosh]

Thanks @adhulipa merging