compiler error when trying to get random key from AA

[mark]

I have this code:

import std.random;
import std.stdio;
void main()
{
     auto aa = ["one": 1, "two": 2, "three": 3];
     writeln(aa);
     auto rnd = rndGen;
     auto word = aa.byKey.choice(rnd);
     writeln(word);
}

And in the D playground it gives this error:

onlineapp.d(8): Error: template std.random.choice cannot deduce 
function from argument types !()(Result, 
MersenneTwisterEngine!(uint, 32LU, 624LU, 397LU, 31LU, 
2567483615u, 11LU, 4294967295u, 7LU, 2636928640u, 15LU, 
4022730752u, 18LU, 1812433253u)), candidates are:
/dlang/dmd/linux/bin64/../../src/phobos/std/random.d(2599):       
  choice(Range, RandomGen = Random)(auto ref Range range, ref 
RandomGen urng)
   with Range = Result,
        RandomGen = MersenneTwisterEngine!(uint, 32LU, 624LU, 
397LU, 31LU, 2567483615u, 11LU, 4294967295u, 7LU, 2636928640u, 
15LU, 4022730752u, 18LU, 1812433253u)
   must satisfy the following constraint:
        isRandomAccessRange!Range
/dlang/dmd/linux/bin64/../../src/phobos/std/random.d(2609):       
  choice(Range)(auto ref Range range)

I am treating aa as a set and want to pick a random word from it.
What am I doing wrong?

I'm sorry I can't give a link to this code in the D playground 
but the URL in the web browser is just https://run.dlang.io/ and 
when I click Shorten to get a URL nothing seems to happen (using 
Firefox on Linux).