Reduce screenshot width

lib/server/controllers/apiController.js

@@ -78,7 +78,7 @@ var ApiController = function(app) {
             if (run.params.screenshot) {
                 
                 // Replace the empty promise created earlier with Q.resolve()
-                screenshotPromise = screenshot.toThumbnail(600)
+                screenshotPromise = screenshot.toThumbnail(400)
                 
                     // Read screenshot
                     .then(function(screenshotBuffer) {