Package with Ruby 2.1

Previously, the Gemfile of the project assumed that all work was being
done against Ruby 1.9.x.  The CI tests ran successfully on the 2.1
line because they excluded the version-specific debug gems with a
--without debug.  The instructions (and indeed good user experience)
did not ask users to do this, so when bundle install was run in a
non-1.9 Ruby runtime, the gems would not install.

This change updates the Gemfile to install version-specific debug gems
allowing development against 1.9.x, 2.0.x, and 2.1.x.
Spring Boot 1.1.0

Previously, auto-reconfiguration did not work on Spring Boot
applications.  With the upcoming releases of Spring Boot 1.1.0.RELEASE
and Java Buildpack Auto-reconfiguration 1.0.0.RELEASE, this will no
longer be the case.  This change updates the buildpack to work with
Spring Boot 1.1.0.RELEASE and later.

[#49695439]