MINOR: Fix broken JMX URL in docs

[wj1918]

The "Monitoring and Management Using JMX Technology" link on the operations page is broken because of a missing double quote in the html a tag.

1. Open http://kafka.apache.org/documentation/#operations and search for "JMX Technology"
2. Click the "Monitoring and Management Using JMX Technology" link, you will get "Page not found
   " error
3. notice the URL in the browser address bar, there is a extra double quote at end of the URL https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html"

[wj1918]

duplicate with #8587