Add sps to visual testing

tests/validation/config.json

@@ -2,6 +2,12 @@
   "root": "https://rawgit.com/BabylonJS/Website/master",
   "tests": [
     {
+      "title": "Solid particle system",
+      "playgroundId": "#WCDZS#2",
+      "renderCount": 150,
+      "referenceImage": "sps.png"
+    },
+    {
       "title": "Simulate pointer",
       "playgroundId": "#8MGKWK#78",
       "referenceImage": "simulatePointer.png"