(refactor): move build configs into test/build-config/

- having the build configs in app root made it kind of seem like they
  were being used to produce the library's export, but they're solely
  used for testing purposes
  - so moving them into test/ seems to make sense to me

- also to declutter app root similar to previous commits

- use process.cwd() in webpack config as __dirname is no longer app
  root, but process.cwd() still is as it's still called from
  package.json scripts

package.json

@@ -41,8 +41,8 @@
     "test": "npm run clean && npm run browserify && npm run webpack && ava",
     "test:browserify": "npm run browserify && ava test/browserify.spec.js",
     "test:webpack": "npm run webpack && ava test/webpack.spec.js",
-    "browserify": "node browserify.config.js",
-    "webpack": "webpack",
+    "browserify": "node test/build-config/_browserify.config.js",
+    "webpack": "webpack --config test/build-config/_webpack.config.js",
     "clean": "rm -rf build/ && mkdir build/"
   },
   "ava": {

webpack.config.js → test/build-config/_webpack.config.js

@@ -3,7 +3,7 @@ const path = require('path')
 module.exports = {
   entry: './test/utils/webpack/_export-to-window.js',
   output: {
-    path: path.join(__dirname, '/build/'),
+    path: path.join(process.cwd(), '/build/'),
     filename: 'webpack.bundle.js',
     library: 'Physijs',
     libraryTarget: 'umd'
@@ -14,6 +14,6 @@ module.exports = {
   externals: /^three$/,
   // don't parse ammo
   module: {
-    noParse: path.join(__dirname, '/vendor/ammo.js')
+    noParse: path.join(process.cwd(), '/vendor/ammo.js')
   }
 }