Merge pull request aframevr#1651 from donmccurdy/typo-register-primitive

Fix typo in registerPrimitive

src/index.js

@@ -25,7 +25,7 @@ var AScene = require('./core/scene/a-scene');
 var components = require('./core/component').components;
 var registerComponent = require('./core/component').registerComponent;
 var registerGeometry = require('./core/geometry').registerGeometry;
-var registerPrimitive = require('./extras/primitives/primitives').registerPrimitives;
+var registerPrimitive = require('./extras/primitives/primitives').registerPrimitive;
 var registerShader = require('./core/shader').registerShader;
 var registerSystem = require('./core/system').registerSystem;
 var shaders = require('./core/shader').shaders;