Fix case typo: drawbuffers should be drawBuffers

src/renderers/webgl/WebGLPrograms.js

@@ -281,7 +281,7 @@ function WebGLPrograms( renderer, extensions, capabilities ) {
 
 			extensionDerivatives: material.extensions && material.extensions.derivatives,
 			extensionFragDepth: material.extensions && material.extensions.fragDepth,
-			extensionDrawbuffers: material.extensions && material.extensions.drawbuffers,
+			extensionDrawbuffers: material.extensions && material.extensions.drawBuffers,
 			extensionShaderTextureLOD: material.extensions && material.extensions.shaderTextureLOD,
 
 			rendererExtensionFragDepth: isWebGL2 || extensions.get( 'EXT_frag_depth' ) !== null,