Try to fix Travis builds

[Kmaschta]

There is an issue with the package [email protected], see ahmadnassri/node-har-validator#113

> npm ls har-validator
[email protected] /home/kmaschta/Projects/Inist-CNRS/lodex
├─┬ [email protected]
│ └─┬ [email protected]
│   └── [email protected] 
└─┬ [email protected]
  └── [email protected]

I had to rollback the version of request in order to fix the build. We'll what that request upgrade its versions to fix that.