Update the psq library

[fufexan]

I've tried building the project, but it fails with this log

error: builder for '/nix/store/gj22iyvsikagh72v02790h0cv27l5fl6-ocaml4.12.0-fsq-unstable-2019-09-17.drv' failed with exit code 1;
       last 10 log lines:
       > 76 |                 psq = PsqK.adjust (fun p -> p - d) k t.psq;
       >                                        ^^^^^^^^^^^^^^^^
       > Error: This expression should not be a function, the expected type is PsqK.k
       >     ocamlopt lib/.fsq.objs/native/fsq.{cmx,o} (exit 2)
       > (cd _build/default && /nix/store/28nfnd70f17y2vd3rdihxx8ws3p6i1p2-ocaml-4.12.0/bin/ocamlopt.opt -w -40 -g -I lib/.fsq.objs/byte -I lib/.fsq.objs/native -I /nix/store/vbvl3ggqx588kwdwf380648almyp4wfq-ocaml4.12.0-psq-0.2.0/lib/ocaml/4.12.0/site-lib/psq -I /nix/store/vn9cb3m87klnrw8j1ax12dgxi10gdd16-ocaml4.12.0-seq-0.1/lib/ocaml/4.12.0/site-lib/seq -intf-suffix .ml -no-alias-deps -o lib/.fsq.objs/native/fsq.cmx -c -impl lib/fsq.ml)
       > File "lib/fsq.ml", line 76, characters 34-50:
       > 76 |                 psq = PsqK.adjust (fun p -> p - d) k t.psq;
       >                                        ^^^^^^^^^^^^^^^^
       > Error: This expression should not be a function, the expected type is PsqK.k

What I get from that is that some types have changed over time and the new lib expects other calls.

I'm not sure if #1 refers to the usage of the psq library or the fsq one, if it's the latter please let me know. I'm trying to package this library for Nix as with the other repos in this org, but if it's obsolete there's no point.