Errors while opening Reason files after a bs build

Hi!

Thanks for your great Vim config, everything works fine but I've been having issues with Reason recently.

Step to reproduce:

```console
git clone git clone https://github.com/chenglou/reason-react-example.git
cd reason-react-example
npm install
npm run build
mvim .
```
Now open `mvim src/simple/page.re` from NERDTree.

In my case I get this error:

There are a lot more errors as I type and every time I save a Reason file.

I have installed `reason-cli` and everything seems to be installed correctly, for example I have no problems with the VS Code plugin, only with VimBox.

**Note:** If I delete the `.merlin` file, the file is opened without any errors.

Here is the content of my `.merlin` file if it helps:
```
####{BSB GENERATED: NO EDIT
FLG -ppx '/Users/adrien/Projects/reason-react-example/node_modules/bs-platform/bin/reactjs_jsx_ppx_2.exe'
FLG -ppx /Users/adrien/Projects/reason-react-example/node_modules/bs-platform/bin/bsppx.exe
S /Users/adrien/Projects/reason-react-example/node_modules/bs-platform/lib/ocaml
B /Users/adrien/Projects/reason-react-example/node_modules/bs-platform/lib/ocaml
FLG -nostdlib -no-alias-deps -color always -w -40+6+7+27+32..39+44+45
S /Users/adrien/Projects/reason-react-example/node_modules/reason-react/lib/ocaml
B /Users/adrien/Projects/reason-react-example/node_modules/reason-react/lib/ocaml
S /Users/adrien/Projects/reason-react-example/node_modules/bs-director/lib/ocaml
B /Users/adrien/Projects/reason-react-example/node_modules/bs-director/lib/ocaml
S src
B lib/bs/src
S src/retainedProps
B lib/bs/src/retainedProps
S src/todomvc
B lib/bs/src/todomvc
S src/simple
B lib/bs/src/simple
S src/logo
B lib/bs/src/logo
S src/interop
B lib/bs/src/interop
S src/async
B lib/bs/src/async
####BSB GENERATED: NO EDIT}
```

Thanks!

Reproduce the problem in VimBox using the listed reason-react-example commands, then open src/simple/page.re from NERDTree after npm run build. Compare behavior with and without the generated .merlin file and inspect how VimBox handles Reason and .merlin-related paths. Done means Reason files open and save without the reported errors while the project configuration remains usable.

Written by the indexing model from the issue text.