add width-only option for square shape

Author: bendichter

resources/probe.json.schema

@@ -81,6 +81,11 @@
                     "height": { "type": "integer", "minimum": 0 }
                   },
                   "required": ["width", "height"]
+                },
+                {
+                  "type": "object",
+                  "properties": { "width": { "type": "integer", "minimum": 0 } },
+                  "required": ["width"]
                 }
               ]
             }