Use system-dependent line separator when generating a meta model JSON #181

With core.autocrlf = true for git on Windows the meta model file default.json is checked out with CRLF line endings. ObjectBox gradle plugin generates default.json with LF line endings when building a project, so git considers this file to be modified, however in fact the DB scheme is the same.

Maybe it's possible to workaround this using git configuration I'm not aware of, but I suppose it would be preferable to generate line endings that correspond to the current system.

BTW: are you going to open the code of ObjectBox gradle plugin at some future time? 🙂