Use -html4 for javadoc generation

javadoc in our classes don't yet comply to html5 semantics. When
generating javadocs for our project, using JDK 11, we run into
build failures since JDK 11 javadoc tool defaults to html5 output
and is strict if the classes don't comply to the semantics.

The commit here explicitly sets the output to html4 to avoid such
failures, till we fix our javadoc to comply with html5
1 file changed