fix(javadoc): Fix documentation for default batchSize value

[dj-mr]

Motivation:

Correct Javadoc for variable DEFAULT_BATCH_SIZE.

Conformance:

Your commits should be signed and you should have signed the Eclipse Contributor Agreement as explained in https://github.com/eclipse/vert.x/blob/master/CONTRIBUTING.md Please also make sure you adhere to the code style guidelines: https://github.com/vert-x3/wiki/wiki/Vert.x-code-style-guidelines

[dj-mr]

Correct Javadoc for variable DEFAULT_BATCH_SIZE. No Code changes