Revert "Make the rake tasks aware of bundler, negating the need for bundle exec when running rake"

This reverts commit ceb7ef4a307ac597aac1a2d0d3b315a72e2a16e3.
Replaced rubysl-json with c-json

See https://github.com/rubysl/rubysl/pull/8
Merge pull request #1 from iainbeeston/fix_rubinius

Fix travis build for rubinius