always emit deltaX and deltaY for Input.dispatchMouseEvent

Otherwise, the CDP message with the following params:
 {"type":"mouseWheel","x":0,"y":0,"modifiers":0,"deltaY":100}
will result in an error:
 {"code":-32602,"message":"'deltaX' and 'deltaY' are expected for mouseWheel event"}

Fixes #10

fixup/fixup.go

@@ -177,6 +177,13 @@ const ModifierCommand Modifier = ModifierMeta
 							p.AlwaysEmit = true
 						}
 					}
+				case "dispatchMouseEvent":
+					for _, p := range c.Parameters {
+						switch p.Name {
+						case "deltaX", "deltaY":
+							p.AlwaysEmit = true
+						}
+					}
 				}
 			}