Revert "pin pytest to disallow 2.8.4 which breaks tests"

This reverts commit ed48066a3f8e58af58926a17906540213e57f88e.
diff --git a/dev-requirements.txt b/dev-requirements.txt
index 9aca5dd..c409ff9 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -7,7 +7,7 @@
 pep8-naming
 pretend
 pyasn1_modules
-pytest!=2.8.4
+pytest
 requests
 sphinx==1.3.1
 sphinx_rtd_theme
diff --git a/setup.py b/setup.py
index 43fe17e..19f1e66 100644
--- a/setup.py
+++ b/setup.py
@@ -59,7 +59,7 @@
 
 # If you add a new dep here you probably need to add it in the tox.ini as well
 test_requirements = [
-    "pytest!=2.8.4",
+    "pytest",
     "pretend",
     "iso8601",
     "hypothesis",
diff --git a/tox.ini b/tox.ini
index cf899b7..63f1e4b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,7 +7,7 @@
     coverage
     iso8601
     pretend
-    pytest!=2.8.4
+    pytest
     hypothesis>=1.11.4
     pyasn1_modules
     ./vectors