breaking change in yojson causing build to fail

[joprice]

Version 2.0.0 of yojson removed biniou, which causes the compiler error below. There is a lower bound on yojson in the opam files, but no upper bound. Pinning yojson locally to 1.7.0 allows the build to work for me.

File "src/endpoints_j.ml", line 40, characters 11-13:
  40 |   write__2 ob x;
Error: This expression has type Bi_outbuf.t
       but an expression was expected of type Buffer.t