LegacyPBR only when needed

materialsLibrary/materials/pbr/babylon.pbrMaterial.ts

@@ -823,7 +823,7 @@ module BABYLON {
 
                 // Legacy browser patch
                 var shaderName = "pbr";
-                if (scene.getEngine().getCaps().standardDerivatives) {
+                if (!scene.getEngine().getCaps().standardDerivatives) {
                     shaderName = "legacypbr";
                 }
                 var join = this._defines.toString();