added try except to urllib2 call for cal data

gitfiti.py

@@ -167,7 +167,12 @@ def load_images(img_names):
 def get_calendar(username, base_url='https://github.com/'):
     """retrieves the github commit calendar data for a username"""
     url = base_url + 'users/' + username + '/contributions_calendar_data'
+    try:
         page = urllib2.urlopen(url)
+    except (urllib2.HTTPError,urllib2.URLError) as e:
+        print "There was a problem fetching data from {0}".format(url)
+        print e
+        raise SystemExit
     return json.load(page)
 
 def max_commits(input):