Bumpmap materials fix

<h3> Issue

https://github.com/MasDennis/Rajawali/issues/419

`BumpmapMaterial` and`BumpmapPhongMaterial` were throwing exceptions when used with a `DirectionalLight`. This was being caused by not using the varying `vAttenuation` within the vertex shader.

<h3> Method

Set `vAttenuation[i] = 1.0`in the fragment shader when a `DirectionalLight` is illuminating the object.

````java
            } else if(light.getLightType() == ALight.DIRECTIONAL_LIGHT) {
                vc.append("vAttenuation").append(i).append(" = 1.0;\n");
````

<h3> Usage

No change to usage. It should just work now.