jazzy: Cannot use --swift-version with swift.org toolchain

$ jazzy --swift-version DEVELOPMENT-SNAPSHOT-2016-06-06-a
/Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:164:in `block in <class:Config>': jazzy only supports Swift 2.0 or later. (RuntimeError)
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:36:in `instance_exec'
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:36:in `set'
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:55:in `block in attach_to_option_parser'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1364:in `call'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1364:in `block in parse_in_order'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1351:in `catch'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1351:in `parse_in_order'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1345:in `order!'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1437:in `permute!'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/optparse.rb:1459:in `parse!'
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:368:in `parse_command_line'
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/lib/jazzy/config.rb:326:in `parse!'
    from /Library/Ruby/Gems/2.0.0/gems/jazzy-0.7.0/bin/jazzy:15:in `<top (required)>'
    from /usr/local/bin/jazzy:23:in `load'
    from /usr/local/bin/jazzy:23:in `<main>'

However, this does work:

$ TOOLCHAIN_DIR=/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2016-06-06-a.xctoolchain jazzy

I would like to be able to use a swift.org toolchain with --swift-version, or swift_version: in .jazzy.yml