Fix Bundler version to 1.17.0

[enricostano]

We now use latest in https://github.com/coopdevs/timeoverflow-provisioning/blob/master/roles/common/tasks/ruby.yml#L5

For 2 reasons:

1. Because in Gemfile.lock we set a version < 2.0
2. Because rails 4.2.11 has bundler < 2.0, >= 1.3.0 set as dependency, and we use that Rails version

[enricostano]

https://github.com/coopdevs/timeoverflow-provisioning/blob/master/roles/common/tasks/ruby.yml#L5 is not used.... we need to find a better way to install the correct version of Bundler. Probably after we install rbenv...

[enricostano]

We actually don't use the ruby.yml task....

$ git grep 'ruby.yml'
$