fix: relax camera focal to prevent holes
fix: relax camera focal to prevent holes

Summary:
This PR aims at relaxing a bit the focal of `synthetic_scene` : as it was too long (0.9), this was causing many tracks on the walls not to be visible by the camera, thus making reconstruction very flaky.

This could be seen as holes on the walls in the reconstructed scene : ratio of reconstructed points was low (< 0.8 average)

Reviewed By: paulinus

Differential Revision: D25806564

fbshipit-source-id: b42c591454c77bafe40a45134357cebe96356a5e

mapillary/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM,oscarlorentzon/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM