fix: sometimes .trees['app'] is a string, and sometimes a node.

lib/colocate-namespace.js

@@ -1,3 +1,5 @@
+const path = require('path');
+
 const Funnel = require('broccoli-funnel');
 const Merge = require('broccoli-merge-trees');
 const StyleManifest = require('broccoli-style-manifest');
@@ -34,15 +36,16 @@ class ColocatedStyles {
   }
 
   projectNode(app) {
-    const projectPath = this.isAddon ? [
-      app.root,
-      app.treePaths['addon'],
-    ].join('/') : [
-      app.project.root,
-      (app.app || app).trees['app'],
-    ].join('/');
-
-    return new Funnel(projectPath);
+    if (this.isAddon) {
+      return new Funnel(path.join(app.root, app.treePaths['addon']));
+    } else {
+      const appTree = (app.app || app).trees['app'];
+      if (typeof appTree === 'string') {
+        return new Funnel(path.join(app.project.root, appTree));
+      } else {
+        return appTree;
+      }
+    }
   }
 }