fix charts

Author: gregimba

README.md

@@ -14,3 +14,4 @@ Z = zillow.Zillow()
 
 ## GetChart
 [Params](https://www.zillow.com/howto/api/GetChart.htm)
+`Z.GetChart("48749425","dollar",600,300,"10years")`

zillow.py

@@ -32,11 +32,11 @@ def GetZestimate(self, zpid):
     def GetChart(self,zpid,unit_type, width, height, duration):
         data = {'zws-id' : self.ZWSID,
                 'zpid' : zpid,
-                'unit_type' : unit_type,
+                'unit-type' : unit_type,
                 'width' : width,
                 'height' : height,
-                'duration' : duration}
-        response = requests.get(base + "GetChart.htm",params=data)
+                'chartDuration' : duration}
+        response = requests.get(self.base + "GetChart.htm",params=data)
 
         if response.status_code == 200:
             return xmltodict.parse(response.text)