workflows 0.1.2

• When using a formula preprocessor with add_formula(), workflows now uses
  model-specific information from parsnip to decide whether to expand
  factors via dummy encoding (n - 1 levels), one-hot encoding (n levels), or
  no expansion at all. This should result in more intuitive behavior when
  working with models that don't require dummy variables. For example, if a
  parsnip rand_forest() model is used with a ranger engine, dummy variables
  will not be created, because ranger can handle factors directly (#51, #53).