Set material.needsUpdate=true if side switches from/to double

[takahirox]

Description:

This PR sets material.needsUpdate=true to update shader
if material.side switches from/to THREE.DoubleSide.

Three.js code

• https://github.com/mrdoob/three.js/blob/fc1159a6415dd7c833b2bf7ee41374c2b2a6cc6a/src/renderers/shaders/ShaderChunk/normal_flip.glsl#L1
• https://github.com/mrdoob/three.js/blob/4a77f64f1479042e9b76734d14acc1ea4f9bfd17/src/renderers/webgl/WebGLPrograms.js#L197
• https://github.com/mrdoob/three.js/blob/adb7979ddf7c0fa678084add5c076172de68e217/src/renderers/webgl/WebGLProgram.js#L351

Changes proposed:

• set material.needsUpdate=true if side switches from/to double
• add a test for that

[dmarcos]

Thanks!