Complete doubleArray challenge

When using higher level functions on arrays (map, reduce, etc) ensure
that you return BOTH the function call and each individual result within
the anonymous function you are using.

RETURN(1) array.map(function(element) {
            RETURN(2) element * 2;
          });

Return 1, returns the value of the newly generated array.
Return 2, returns each individual mutated value into the new array which
is provided in the first return to the calling entity.