Improve error message formatting

[michaelweylandt]

For objects with multiple S3 classes, only
print the first in errors/warnings thrown
by the default methods of tidy, augment, & glance

Previous behavior:

# my_fit is the output of glmnet(X, y)
> augment(my_fit)
Error: augment doesn't know how to deal with data of class elnetglmnet

New behavior:

> augment(my_fit)
Error: augment doesn't know how to deal with data of class elnet

[michaelweylandt]

Both Travis and AppVeyor failed this PR, but I think those are not because of my changes:

• AppVeyor is complaining about something related to the survival package:

Running the tests in 'tests/test-all.R' failed.
Last 13 lines of output:
  1/1 mismatches
  [1] 8 - 9 == -1
  
  -- 2. Failure: glance.survreg works (@test-survival.R#145)  --------------------
  ncol(o) not equal to `exp.col`.
  1/1 mismatches
  [1] 8 - 9 == -1
  
  == testthat results  ===========================================================
  OK: 1424 SKIPPED: 0 FAILED: 2
  1. Failure: survreg tidiers work (@test-survival.R#128) 
  2. Failure: glance.survreg works (@test-survival.R#145) 
  
  Error: testthat unit tests failed
  Execution halted
* DONE

• Travis timed out in the build stage before it could even start testing

[alexpghayes]

Thanks!

[github-actions]

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