Fix 'false' to string.

[vjache]

I have encountered a problem when tried to generate default config from riak.schema at:

...
%% VM scheduler collapse, part 2 of 2                                                                                                                                                          
{mapping, "erlang.schedulers.compaction_of_load", "vm_args.+scl", [
  {default, false},
  merge
]}.
...

[ates]

Faced with the same problem, do you plan to merge this pull request ?