Fixed Error

[KotaroInaba]

I got the following error message and thus I tried to fix it by referring other dune files.

File "dune", line 5, characters 7-22: 5 | (pps ppx_deriving.eq ppx_deriving.show))) ^^^^^^^^^^^^^^^ Hint: try: dune external-lib-deps --missing @runtest make: *** [Makefile:4: test] Error 1