Declares the template method as final (Issue 1099)

[dgruntz]

As described in Issue #1099 it is recommended to declare the template method as final.
This pull request changes the implementation in the sample code of the template method pattern.

This change is applied both in the sample code and in the documentation.

Moreover, the tests was adjusted. As Mockito has problems with final methods, the Mockito dependency had to be changed from mockito-core to mockito-inline.

The tests pass:

[INFO] Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.005 s - in com.iluwatar.templatemethod.SubtleMethodTest
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 11, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  3.938 s
[INFO] Finished at: 2022-10-05T11:21:34+02:00
[INFO] ------------------------------------------------------------------------

[iluwatar]

This looks perfect. Well done @dgruntz 👍😄

@all-contributors please add @dgruntz for code

[allcontributors]

@iluwatar

@dgruntz already contributed before to code