Fixes missing string sub.

tweepy/api.py

@@ -1244,7 +1244,7 @@ class API(object):
         if f is None:
             try:
                 if os.path.getsize(filename) > (max_size * 1024):
-                    raise TweepError('File is too big, must be less than kb.' % max_size)
+                    raise TweepError('File is too big, must be less than %skb.' % max_size)
             except os.error:
                 raise TweepError('Unable to access file')
 
@@ -1253,7 +1253,7 @@ class API(object):
         else:
             f.seek(0, 2)  # Seek to end of file
             if f.tell() > (max_size * 1024):
-                raise TweepError('File is too big, must be less than kb.' % max_size)
+                raise TweepError('File is too big, must be less than %skb.' % max_size)
             f.seek(0)  # Reset to beginning of file
             fp = f