Run Coveralls only in Travis CI
Run Coveralls only in Travis CI

We were seeing a log message when running specs locally

```
[Coveralls] Set up the SimpleCov formatter.
[Coveralls] Using SimpleCov's 'rails' settings.
```

As Coveralls is mainly used in Travis CI, we do not need to load it in
every spec run

AyuntamientoMadrid/consul,AyuntamientoMadrid/consul,AyuntamientoPuertoReal/decidePuertoReal,lalibertad/consul,deivid-rodriguez/participacion,usabi/consul_san_borondon,deivid-rodriguez/participacion,usabi/consul_san_borondon,lalibertad/consul,AyuntamientoMadrid/consul,CDJ11/CDJ,AjuntamentdeCastello/consul,usabi/consul_san_borondon,consul/consul,AyuntamientoPuertoReal/decidePuertoReal,AyuntamientoPuertoReal/decidePuertoReal,consul/consul,lalibertad/consul,usabi/consul_san_borondon,AyuntamientoMadrid/participacion,AjuntamentdeCastello/consul,consul/consul,CDJ11/CDJ,AyuntamientoMadrid/participacion,consul/consul,AjuntamentdeCastello/consul,AyuntamientoMadrid/participacion,CDJ11/CDJ,AyuntamientoMadrid/consul,consul/consul,AjuntamentdeCastello/consul,deivid-rodriguez/participacion,AyuntamientoMadrid/participacion,CDJ11/CDJ,lalibertad/consul,deivid-rodriguez/participacion