Fix InterleavedBuffer accessors

src/core/InterleavedBuffer.js

@@ -21,17 +21,17 @@ function InterleavedBuffer( array, stride ) {
 
 }
 
-Object.assign( InterleavedBuffer.prototype, {
+Object.defineProperty( InterleavedBuffer.prototype, "needsUpdate", {
 
-	constructor: InterleavedBuffer,
+	set: function(value) { if ( value === true ) this.version ++; }
 
-	isInterleavedBuffer: true,
+});
 
-	set needsUpdate( value ) {
+Object.assign( InterleavedBuffer.prototype, {
 
-		if ( value === true ) this.version ++;
+	constructor: InterleavedBuffer,
 
-	},
+	isInterleavedBuffer: true,
 
 	setArray: function ( array ) {