Docker compose up 'Exec format error' loading a library

I'm developing a multi-module docker nodejs app with docker-compose. There's an issue with the natural node package needed by a module. It seems that it can't exec it. I tried to rebuild it on the fly with a RUN command, but nothing changed. Here's the log when trying to run docker-compose up:

web_1         | /app/web-server/node_modules/natural/lib/natural/classifiers/classifier.js:32
web_1         |     if (e.code !== 'MODULE_NOT_FOUND') throw e;
web_1         |                                        ^
web_1         |
web_1         | Error: Error loading shared library /app/web-server/node_modules/webworker-threads/build/Release/WebWorkerThreads.node: Exec format error
web_1         |     at Error (native)
web_1         |     at Object.Module._extensions..node (module.js:597:18)
web_1         |     at Module.load (module.js:487:32)
web_1         |     at tryModuleLoad (module.js:446:12)
web_1         |     at Function.Module._load (module.js:438:3)
web_1         |     at Module.require (module.js:497:17)
web_1         |     at require (internal/module.js:20:19)
web_1         |     at bindings (/app/web-server/node_modules/bindings/bindings.js:81:44)
web_1         |     at Object.<anonymous> (/app/web-server/node_modules/webworker-threads/index.js:1:105)
web_1         |     at Module._compile (module.js:570:32)
web_1         |     at Object.Module._extensions..js (module.js:579:10)
web_1         |     at Module.load (module.js:487:32)
web_1         |     at tryModuleLoad (module.js:446:12)
web_1         |     at Function.Module._load (module.js:438:3)
web_1         |     at Module.require (module.js:497:17)
web_1         |     at require (internal/module.js:20:19)

Here's the package.json:

{
  "name": "realaffinities",
  "version": "1.0.0",
  "description": "",
  "main": "server/Server.js",
  "keywords": [],
  "author": "",
  "license": "GPL-3.0",
  "dependencies": {
    "async": "^2.5.0",
    "big-integer": "^1.6.23",
    "body-parser": "1.9.0",
    "express": "^4.15.3",
    "express-validator": "^3.2.1",
    "knex": "^0.13.0",
    "mysql": "^2.14.1",
    "natural": "^0.5.4",
    "twit": "^2.2.9",
    "url-exists": "^1.0.3",
    "nodemon": "^1.11.0"
  },
  "devDependencies": {
    "grunt": "^1.0.1",
    "grunt-express-server": "^0.5.3",
    "mocha": "^3.4.2",
    "supertest": "^3.0.0",
    "bcrypt": "1.0.2"
  },
  "scripts": {
    "test": "mocha web-server/test",
    "start": "node server/Server.js"
  }
}

My dockerfile:

FROM node:6.11-alpine

EXPOSE 3000
ENV NODE_ENV development
RUN mkdir /app
WORKDIR /app

# add package.json and run npm install before adding the rest of the files
# this way, you only run npm install when package.json changes
ADD /web-server/package.json /app/package.json

RUN apk add --no-cache make gcc g++ python

RUN npm install -g mocha
RUN npm install

I don't know whether it's an issue of this particular node package or a knowledge lack of mine. If I run the same application locally on my mac without docker, it doesn't encounter this problem.