Fixed category in check_argument function

{
"category": "windows", 
"status": false, 
"return": "0x00000000", 
"timestamp": "2013-05-15 21:36:32,491", 
"thread_id": "1400", 
"repeated": 0, 
"api": "FindWindowA", 
"arguments": [
 {
   "name": "ClassName", 
   "value": "OLLYDBG"
 }, 
 {
   "name": "WindowName", 
   "value": ""
 }
]
}