Remove lxml >=3.8.0 dependency.

Cody Piersall · Cody Piersall · commit 3688a3b60de1 · 2017-12-15T20:47:10.000Z
The version dependency makes it hard to install nbextensions on certain platforms (e.g. ARM). See Issue #1172.
diff --git a/setup.py b/setup.py
@@ -72,7 +72,7 @@ def main():
             'pyyaml',
             'tornado',
             'traitlets >=4.1',
-            'lxml >=3.8.0'
+            'lxml'
         ],
         extras_require={
             'test': [
