Resize a generator
Returns a generator spec that draws from source with the
size (number of elements/rows) of nested vector, list, and df generators
overridden to n. Generators that do not carry their own
size are unaffected.
source (Dict): The generator to
resize.
n (Int): New size for nested
vector/list/df generators.
A generator spec.
g = prop_resize(prop_gen_vector(prop_gen_int(), 3), 20)