Update js_of_ocaml to 5.5.2

[WardBrian]

The recent 5.5 release of js_of_ocaml featured some pretty big improvements to the dead code elimination phase which makes the produced file smaller. On my machine, this is a nearly 15% improvement:

-r--r--r--  1 brian brian 1873308 Dec  8 10:13 stancjs.4.1.0.bc.js
-r--r--r--  1 brian brian 1608773 Dec  8 10:18 stancjs.5.5.2.bc.js

In terms of speed, it seems to be essentially the same, maybe slightly faster, but definitely within the range that the noise on my machine makes benchmarking unable to tell the difference between the two versions.

Submission Checklist

• [x] Run unit tests
• Documentation
  • [ ] If a user-facing facing change was made, the documentation PR is here:
  • [x] OR, no user-facing changes were made

Release notes

Updated js_of_ocaml to version 5.5.2

Copyright and Licensing

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the BSD 3-clause license (https://opensource.org/licenses/BSD-3-Clause)

[codecov[bot]]

Codecov Report

Merging #1381 (3433c6a) into master (992ff90) will increase coverage by 89.93%. The diff coverage is n/a.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1381 +/- ## =========================================== + Coverage 0 89.93% +89.93% =========================================== Files 0 63 +63 Lines 0 10699 +10699 =========================================== + Hits 0 9622 +9622 - Misses 0 1077 +1077 ``` [see 63 files with indirect coverage changes](https://app.codecov.io/gh/stan-dev/stanc3/pull/1381/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=stan-dev)