It doesn't see a devDependencies executable on npm 5.4.1

I have a package with this `package.json`:

```json
{
"name": "@perevezentsev/decode-video",
"version": "3.0.0",
"description": "Decodes video using ffmpeg into raw RGBA32 frames",
"main": "./built/index.js",
"scripts": {
"build": "tsc || true",
"build:watch": "tsc --watch",
"test": "tape ./built/**/*.test.js | tap-spec",
"start": "node ./example/",
"postinstall": "postinstall-build ./built"
},
"author": "Ivan Perevezentsev ",
"license": "UNLICENSED",
"private": true,
"dependencies": {
"@types/node": "^8.0.28",
"chunking-streams": "0.0.8",
"fluent-ffmpeg": "^2.1.2",
"mkdirp": "^0.5.1",
"png-async": "^0.9.2",
"postinstall-build": "^5.0.1",
"rimraf": "^2.6.1"
},
"devDependencies": {
"eslint": "^4.2.0",
"eslint-config-airbnb-base": "^11.2.0",
"eslint-plugin-import": "^2.7.0",
"tap-spec": "^4.1.1",
"tape": "^4.8.0",
"typescript": "^2.5.2"
}
}
```

When running `npm install` in a project using this package, `postinstall-build` is triggered correctly, but npm `build` script doesn't see TypeScript compiler which is in the `devDependencies`:

```
➜ test npm i -S ../video-decoder2

> @perevezentsev/decode-video@3.0.0 postinstall /home/vanya/Documents/prog/1.videonow/test/node_modules/@perevezentsev/decode-video
> postinstall-build ./built

postinstall-build:
This version of npm (5.4.1) may not be compatible with postinstall-build! There
are outstanding bugs in certain versions of npm that prevent it from working with
postinstall-build. See https://github.com/exogen/postinstall-build#bugs-in-npm
for more information.

> @perevezentsev/decode-video@3.0.0 build /home/vanya/Documents/prog/1.videonow/video-decoder2
> tsc || true

sh: 1: tsc: not found
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN @perevezentsev/test@1.0.0 No description
npm WARN @perevezentsev/test@1.0.0 No repository field.

+ @perevezentsev/decode-video@3.0.0
added 24 packages in 9.097s
➜ test npm -v
5.4.1
```

Are there plans to fix this for this version of npm?