Incorrect reference to `stop` method in documentation

[fmbenhassine]

The section Stopping a Job Manually for Business Reasons has an incorrect reference to a stop method in the JobLauncher interface:

Spring Batch provides a stop() method through the JobLauncher interface, but this is really for use by the operator rather than the application programmer.

JobLauncher has no stop method, the doc should rather say "through the JobOperator interface".

[fmbenhassine]

Resolved with #3696 .