Fix travis on ruby 2.2
Fix travis on ruby 2.2

This fixes the following issue:

```
 The program 'bundle' is currently not installed. To run
'bundle' please ask your administrator to install the package 'bundler'.

```

Seems like the issue is the bundler 2.0 is not compatible with
ruby < 2.3.0

Dynflow/dynflow,Dynflow/dynflow,Dynflow/dynflow,Dynflow/dynflow