`fit` only works properly when `MASS` is loaded

[dmalzl]

Describe the bug
It seems to me that fitting the model only works properly when the MASS packages is loaded in addition to chromunity (this is done in the tutorial btw. but it is weird nevertheless). When only loading chromunity and calling fit the function returns a NULL as the model. Only after loading MASS I get a proper model back. The reason for this probably is that glm.nb is not found and the tryCatch construct simply swallows the error. In my opinion this should not happen as MASS is also loaded by chromunity

To Reproduce

1. do all the steps of the tutorial but do not load MASS
2. try to fit the model
3. get NULL as the model
4. only after loading MASS manually the model is fit properly

Expected behavior
fit should work out of the box

[jameson-orvis]

Thank you for pointing this out, MASS should be listed as a dependency.