Fixes typo

Author: palnabarun

mplaltair/_axis.py

@@ -47,7 +47,7 @@ def convert_axis(ax, chart):
     if chart.to_dict().get('config').get('scale'):
         raise NotImplementedError
 
-    for enc_channel, enc_spec in chart.to_dict['encoding']:
+    for enc_channel, enc_spec in chart.to_dict()['encoding']:
         if enc_channel in ['x', 'y']:
             _set_title(ax, enc_channel, enc_spec)
             _set_ticks(ax, enc_channel, enc_spec)