Pin pillow to < 5.4 to fix doc build

dstansby · dstansby · commit b055cb72803f · 2019-01-02T15:28:01.000Z
diff --git a/doc-requirements.txt b/doc-requirements.txt
@@ -11,6 +11,6 @@ colorspacious
 ipython
 ipywidgets
 numpydoc>=0.8
-pillow>=3.4
+pillow>=3.4,<5.4
 sphinx-gallery>=0.2
 sphinx-copybutton
