Fix issue esi-neuroscience#6. Gammatron.m radius is set properly.

Author: jsdpag

arcade/StimServer/classes/Stimuli/Gammatron.m

@@ -77,8 +77,8 @@
         end
 
         function set.radius(obj, radius)
-            obj.shaderWidth = radius;
-            obj.shaderHeight = radius;
+            obj.shaderWidth = 2 * radius;
+            obj.shaderHeight = 2 * radius;
         end