Python 3-only Pyrsistent release broke the universe.

Author: itamarst

hdijupyterutils/requirements.txt

@@ -7,3 +7,5 @@ jupyter>=1
 pandas>=0.17.1
 numpy
 notebook>=4.2
+# Work around broken-on-Python-2 pyrsistent release:
+pyrsistent < 0.17 ; python_version < '3.0'

hdijupyterutils/setup.py

@@ -64,5 +64,7 @@ def version(path):
           'jupyter>=1',
           'pandas>=0.17.1',
           'numpy',
-          'notebook>=4.2'
+          'notebook>=4.2',
+          # Work around broken-on-Python-2 pyrsistent release:
+          "pyrsistent < 0.17 ; python_version < '3.0'",
       ])