Fix npm 2.x build failures for angular-material-source dependency

- Angular-material-source does not have a main node module, its only
  built to ./dist and published via bower. The first attempt to make
  this work with npm 3.x broke (some users) npm 2.x env's.

- This aims to allow building a project that includes this addon for
  npme 2.x and 3.x for all versions of node.

fixes adopted-ember-addons#349

index.js

@@ -106,10 +106,12 @@ module.exports = {
       'components/dialog/dialog-theme.scss'
     ];
 
-    var pathBase = this.project.nodeModulesPath;
-    var angularMaterialPath =  'angular-material-source/src';
+    // This.nodeModulesPath is relative to either this addon or an ember project
+    // Its use is analogous to path.dirname(require.resolve('angular-material-source'))
+    // w/ diff being it resolves without relying on upstream package exporting a main module
+    var pathBase = path.resolve(this.nodeModulesPath, 'angular-material-source', 'src');
 
-    var angularScssFiles = new Funnel(path.join(pathBase,angularMaterialPath), {
+    var angularScssFiles = new Funnel(pathBase, {
       files: scssFiles,
       destDir: 'angular-material',
       annotation: 'AngularScssFunnel'