remove redundant runner.isFixed from examples

Author: liabru

examples/stress3.js

@@ -34,9 +34,7 @@ Example.stress3 = function() {
     Render.run(render);
 
     // create runner
-    var runner = Runner.create({
-        isFixed: true
-    });
+    var runner = Runner.create();
     Runner.run(runner, engine);
 
     // add bodies

examples/stress4.js

@@ -35,9 +35,7 @@ Example.stress4 = function() {
     Render.run(render);
 
     // create runner
-    var runner = Runner.create({
-        isFixed: true
-    });
+    var runner = Runner.create();
 
     Runner.run(runner, engine);