Changed gradle documentation export docker context from --jib.dockerDir  to --targetDir (#661)
Changed gradle documentation export docker context from --jib.dockerDir  to --targetDir (#661)

In #499, the option from gradle to export the docker context was changed, but it wasn't reflected in the docs.
GoogleContainerTools/jib,GoogleContainerTools/jib,GoogleContainerTools/jib,GoogleContainerTools/jib