Had to manually add jaxb-api dependency in order for sphinx4-core to compile

[jotadepicas]

Hi,
not sure if this is a bug or not, but in order for project sphinx4-core to compile I had to manually edit build.gradle and add the following line:

compile group: 'javax.xml.bind', name: 'jaxb-api', version: '2.4.0-b180830.0359'

I'm using Eclipse 2019-03 (4.11.0) and Java VM zulu-12-amd64 from Azul Systems. I cloned the git repo, imported it with the Eclipse gradle wizard, and got compilation errors not finding the JAXB classes like the one mentioned above.