tidyr 1.1.4

• expand_grid() is now about twice as fast and pivot_wider() is a bit faster
  (@mgirlich, #1130).

• unchop() is now much faster, which propagates through to various functions,
  such as unnest(), unnest_longer(), unnest_wider(), and
  separate_rows() (@mgirlich, @DavisVaughan, #1127).

• unnest() is now much faster (@mgirlich, @DavisVaughan, #1127).

• unnest() no longer allows unnesting a list-col containing a mix of vector
  and data frame elements. Previously, this only worked by accident, and is
  considered an off-label usage of unnest() that has now become an error.