Reformat Javadoc link in reference docs

The links for methods in Javadocs html pages was changed in JDK 11, from dash to brackets for parameter, so any Javadocs built with JDK 11+ conforms to the new format, i.e.:

JDK 11+ new format:

https://tinkerpop.apache.org/javadocs/3.7.0/core/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.html#aggregate(java.lang.String)

JDK 8 format:

https://tinkerpop.apache.org/javadocs/3.7.0/core/org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.html#aggregate-java.lang.String-

All of our current docs follow the old JDK 8 format, which meant that links to specific methods are not working. We could mitigate this by requiring docs to be built on JDK 8, or we could update all of the links in the docs and require doc building to be on JDK 11+.