replace random module with rand (Erlang 19+)

[luc-tielen]

See title, random module is deprecated as of Erlang version 19.
This gives problems when I try working with it when using for example ExCheck:

Small excerpt of the error:

==> triq (compile)
Compiled src/triq_autoexport.erl
Compiling src/triq_dom.erl failed:
src/triq_dom.erl:290: random:uniform/1: the 'random' module is deprecated; use the 'rand' module instead
... (many more similar errors) ...
ERROR: compile failed while processing /tmp/excheck/deps/triq: rebar_abort

Replacing it with the new and better rand module should fix the problem.

See #61.

[walter-weinmann]

See pull request #63.