chore: use npm install version

package.json

@@ -42,14 +42,15 @@
     "coveralls": "^2.11.14",
     "memory-fs": "^0.3.0",
     "mocha": "^3.1.0",
+    "npm-install-version": "^6.0.1",
     "nyc": "^8.3.1",
-    "xo": "^0.16.0",
-    "webpack": "^1.13.2"
+    "webpack": "^1.13.2",
+    "xo": "^0.16.0"
   },
   "scripts": {
     "pretest": "xo",
-    "test:webpack1": "npm i webpack@1 && nyc mocha",
-    "test:webpack2": "npm i webpack@beta && nyc mocha && npm i webpack@1",
+    "test:webpack1": "WEBPACK_VERSION=1 nyc mocha",
+    "test:webpack2": "WEBPACK_VERSION=beta nyc mocha",
     "test": "npm run test:webpack1 && npm run test:webpack2",
     "preversion": "npm run test",
     "version": "git add -A ."

test/helpers/pack.js

@@ -1,7 +1,7 @@
 'use strict';
 
-var webpack = require('webpack');
 var MemoryFileSystem = require('memory-fs');
+var webpack = require('./webpack');
 
 /**
  * Basic in memory compiler, promisified

test/helpers/setup.js

@@ -8,3 +8,4 @@ chai.use(require('chai-as-promised'));
 
 // get path from the './test' directory
 global.getPath = require('path').join.bind(this, __dirname, '..');
+

test/helpers/webpack.js

@@ -0,0 +1,7 @@
+'use strict';
+
+var niv = require('npm-install-version');
+
+var packageName = 'webpack@' + process.env.WEBPACK_VERSION;
+niv.install(packageName);
+module.exports = niv.require(packageName);

test/index.js

@@ -1,10 +1,10 @@
 'use strict';
 
 var assign = require('object-assign');
-var webpack = require('webpack');
 
 var StyleLintPlugin = require('../');
 var pack = require('./helpers/pack');
+var webpack = require('./helpers/webpack');
 
 var configFilePath = getPath('./.stylelintrc');
 var baseConfig = {