test: Pin pytest dependency due to breaking change

A recent change in pytest 4.1 that hasn't propogated to all plugins yet
is causing some failures.

Refs miketheman/pytest-socket#16
Refs pytest-dev/pytest-cov#253

Signed-off-by: Mike Fiedler <[email protected]>

Author: miketheman

Pipfile

@@ -12,7 +12,7 @@ aws-xray-sdk = "*"
 [dev-packages]
 black = "*"
 freezegun = "*"
-pytest = "*"
+pytest = "<4.1"
 pytest-cov = "*"
 "pytest-flake8" = "*"
 pytest-mock = "*"