Fix javadoc issues in maven release build for JDK 11

[RushanNanayakkara]

Describe the issue:
The release build of the wso2-extensions/identity-local-auth-smsotp repository fails while the normal build passes.
This is observed after bumping the JDK version from 1.8 to 11.

How to reproduce:
Trigger a normal build in wso2-extensions/identity-local-auth-smsotp reposiroty
Trigger a release build in wso2-extensions/identity-local-auth-smsotp reposiroty
Observe that the normal build passes while the release build fails.

Expected behavior:
Both builds should pass without issue.

Environment information (Please complete the following information; remove any unnecessary fields) :

• JDK : 11