[WIP] update gemfile

[noraj]

I updated the Gemfile of course since it was not updated for 2 years there are many conflicts and breakings, I indicatd the major breakings changes in comment from version upgrade but there is also conflicts between dependencies.

$ bundle install 
Fetching gem metadata from https://rubygems.org/............
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies...
Bundler could not find compatible versions for gem "json":
  In Gemfile:
    json (~> 2.2.0)

    data_mapper (~> 1.2.0) was resolved to 1.2.0, which depends on
      dm-serializer (~> 1.2.0) was resolved to 1.2.0, which depends on
        json (~> 1.5.4)

Bundler could not find compatible versions for gem "rack":
  In Gemfile:
    rack-ssl (~> 1.4.1) was resolved to 1.4.1, which depends on
      rack

    rack_csrf (~> 2.6.0) was resolved to 2.6.0, which depends on
      rack (>= 1.1.0)

    sinatra (~> 1.4.8) was resolved to 1.4.8, which depends on
      rack (~> 1.5)

    thin (~> 1.7.2) was resolved to 1.7.2, which depends on
      rack (>= 1, < 3)

Anyway it needs an upgrade since #31 shows dependencies are already broken.

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @noraj to sign the Salesforce.com Contributor License Agreement.