jetbrains file probably shouldn't ignore .idea/gradle.xml

[chronodm]

Checking out an IDEA/Gradle project on a new machine always produces a new "unlinked Gradle project" warning, requiring the generation of a new .idea/gradle.xml and the (re)generation of existing module files.

[gtback]

It might be better to file this against https://github.com/github/gitignore, since (I think) that is where joe gets its (his?) data.