Fixing pymssql requirement

Due to current state of pymssql, having to modify the requirement to ensure requirements install works as expected going forward (until pymssql is replaced or support plan is figured out).

Author: Alex Meadows

setup.py

@@ -23,7 +23,7 @@
         "google-compute-engine >= 2.8.13",
         "psycopg2-binary >= 2.8.2",
         "pymysql >= 0.9.3",
-        "pymssql >= 2.1.4",
+        "pymssql <3.0",
         "python-dateutil >= 2.8.0",
         "snowflake-sqlalchemy >= 1.1.13",
         "sqlalchemy >= 1.3.3",