Pin pyrsistent

Summary: Last update started breaking all py27 tests, pinning for now.

Test Plan: BK

Reviewers: alangenfeld, schrockn, nate, sashank

Reviewed By: sashank

Subscribers: sashank

Differential Revision: https://dagster.phacility.com/D4365

python_modules/dagster/setup.py

@@ -61,7 +61,8 @@ def get_version():
             "alembic>=1.2.1",
             "grpcio==1.30.0",  # pinned so that code generated by grpc will work
             "protobuf==3.12.4",  # pinned so that code generated by grpc will work
-            "pyrsistent>=0.14.8",
+            "pyrsistent>=0.14.8,<=0.16.0; python_version < '3'",  # 0.17.0 breaks py2 support
+            "pyrsistent>=0.14.8; python_version >='3'",
             "python-dateutil",
             "requests",
             "rx<=1.6.1",  # 3.0 was a breaking change. No py2 compatability as well.