merl-an loses determinism between compiler versions

[3Rafal]

Found when running error-regression tests:
For merl-an error-regression -s 1 -p test.ml
given test.ml is

let x = 1

let f y = y + 3

merl-an generates different set of commands

5.0.0:

{"sample_id":6,"merlin_id":0,"cmd":"ocamlmerlin server errors -filename test.ml < test.ml","success":true}
{"sample_id":5,"merlin_id":0,"cmd":" ocamlmerlin server locate -look-for ml -position '3:12' -index 0 -filename test.ml < test.ml","success":true}
{"sample_id":2,"merlin_id":0,"cmd":"ocamlmerlin server occurrences -identifier-at '3:12' -filename test.ml < test.ml","success":true}
{"sample_id":1,"merlin_id":0,"cmd":"ocamlmerlin server type-enclosing -position '3:14' -filename test.ml < test.ml","success":true}
{"sample_id":0,"merlin_id":0,"cmd":"ocamlmerlin server case-analysis -start '3:10' -end '3:10' -filename test.ml < test.ml","success":true}

4.14.1:

{"sample_id":6,"merlin_id":0,"cmd":"ocamlmerlin server errors -filename test.ml < test.ml","success":true}
{"sample_id":5,"merlin_id":0,"cmd":" ocamlmerlin server locate -look-for ml -position '3:12' -index 0 -filename test.ml < test.ml","success":true}
{"sample_id":2,"merlin_id":0,"cmd":"ocamlmerlin server occurrences -identifier-at '3:12' -filename test.ml < test.ml","success":true}
{"sample_id":1,"merlin_id":0,"cmd":"ocamlmerlin server type-enclosing -position '3:12' -filename test.ml < test.ml","success":true}
{"sample_id":0,"merlin_id":0,"cmd":"ocamlmerlin server case-analysis -start '3:14' -end '3:14' -filename test.ml < test.ml","success":true}

Diff:

   {"sample_id":6,"merlin_id":0,"cmd":"ocamlmerlin server errors -filename test.ml < test.ml","success":true}
   {"sample_id":5,"merlin_id":0,"cmd":" ocamlmerlin server locate -look-for ml -position '3:12' -index 0 -filename test.ml < test.ml","success":true}
   {"sample_id":2,"merlin_id":0,"cmd":"ocamlmerlin server occurrences -identifier-at '3:12' -filename test.ml < test.ml","success":true}
-  {"sample_id":1,"merlin_id":0,"cmd":"ocamlmerlin server type-enclosing -position '3:14' -filename test.ml < test.ml","success":true}
-  {"sample_id":0,"merlin_id":0,"cmd":"ocamlmerlin server case-analysis -start '3:10' -end '3:10' -filename test.ml < test.ml","success":true}
+  {"sample_id":1,"merlin_id":0,"cmd":"ocamlmerlin server type-enclosing -position '3:12' -filename test.ml < test.ml","success":true}
+  {"sample_id":0,"merlin_id":0,"cmd":"ocamlmerlin server case-analysis -start '3:14' -end '3:14' -filename test.ml < test.ml","success":true}

The difference is pretty small, but it's enough to break tests. I'm not sure if it's worth fixing this, but I'm sure that we should include it in readme/docs.