A dirty solution to make none of my proposed changes could be to use JRuby 9000 to install the gem but keep the dependency on JRuby 1.7:
jruby {
defaultRepositories = false
defaultVersion = '9.1.2.0' // instead of jrubyVersion = 1.7.25
execVersion = '9.1.2.0' // instead of jrubyVersion = 1.7.25
// TODO I'd like to be able to customize the name of the gemInstallDir
}
A first test with an SVG image seems to work, I don't know the implications of this approach though.
Currently installation of prawn-svg fails because Ruby >=2.0 is required.
JRuby 1.7.x supports a bit of Ruby 2.0 but apparently not enough to declare it as supported during gem installation.
Thoughts on this approach?