Update metrics.rb

[toddiuszho]

Text intros with meter named "something", but every reference thereafter uses "thing". Correcting the meter name.

[elasticsearch-release]

Jenkins standing by to test this. If you aren't a maintainer, you can ignore this comment. Someone with commit access, please review this and clear it for Jenkins to run; then say 'jenkins, test it'.

[toddiuszho]

Just signed the CLA.