add missing tornado import

jenshnielsen · jenshnielsen · commit d58e82fbd06a · 2015-11-04T17:50:24.000Z
diff --git a/lib/matplotlib/backends/backend_webagg_core.py b/lib/matplotlib/backends/backend_webagg_core.py
@@ -22,6 +22,7 @@
 import warnings
 
 import numpy as np
+import tornado
 
 from matplotlib.backends import backend_agg
 from matplotlib.figure import Figure
