pipenv: restrict pytest<5.0.0

This prevents a test exception that presents like:

    tests/transform_csl.py:46:
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    fatcat_tools/transforms/csl.py:204: in citeproc_csl
        style_path = get_style_filepath(style)
    .venv/lib/python3.5/site-packages/citeproc_styles/__init__.py:74: in get_style_filepath
        if resource_exists(__name__, independent_style):
    .venv/lib/python3.5/site-packages/pkg_resources/__init__.py:1134: in resource_exists
        return get_provider(package_or_requirement).has_resource(resource_name)
    .venv/lib/python3.5/site-packages/pkg_resources/__init__.py:1404: in has_resource
        return self._has(self._fn(self.module_path, resource_name))
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    self = <pkg_resources.NullProvider object at 0x7f4f38c0bb00>
    path = '/home/bnewbold/code/fatcat/python/.venv/lib/python3.5/site-packages/citeproc_styles/styles/bibtex.csl'

        def _has(self, path):
            raise NotImplementedError(
    >           "Can't perform this operation for unregistered loader type"
            )
    E       NotImplementedError: Can't perform this operation for unregistered loader type

2 files changed, 13 insertions, 5 deletions

diff --git a/python/Pipfile b/python/Pipfile
index 35465d2b..dbc42557 100644
--- a/python/Pipfile
+++ b/python/Pipfile
@@ -8,7 +8,7 @@ verify_ssl = true
 name = "pypi"
 
 [dev-packages]
-pytest = ">=4"
+pytest = ">=4,<5.0.0"
 pytest-pythonpath = "*"
 pytest-pylint = "*"
 ipython = "*"
diff --git a/python/Pipfile.lock b/python/Pipfile.lock
index 1dc40dac..f652313e 100644
--- a/python/Pipfile.lock
+++ b/python/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "9e80bba24c75a7ee72b8ee90abf4efed2a92d647ddd9af5da201c0b5a9bcc529"
+            "sha256": "3017d7be4c149a8cdde2d78f2930853ac5678ef1206f8a5f5caea862f2ae2cce"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -601,6 +601,13 @@
             ],
             "version": "==2.3.3"
         },
+        "atomicwrites": {
+            "hashes": [
+                "sha256:03472c30eb2c5d1ba9227e4c2ca66ab8287fbfbbda3888aa93dc2e28fc6811b4",
+                "sha256:75a9445bac02d8d058d5e1fe689654ba5a6556a1dfd8ce6ec55a0ed79866cfa6"
+            ],
+            "version": "==1.3.0"
+        },
         "attrs": {
             "hashes": [
                 "sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c",
@@ -754,6 +761,7 @@
                 "sha256:b84b238cce0d9adad5ed87e745778d20a3f8487d0f0cb8b8a586816c7496458d",
                 "sha256:c833ef592a0324bcc6a60e48440da07645063c453880c9477ceb22490aec1564"
             ],
+            "markers": "python_version > '2.7'",
             "version": "==8.0.2"
         },
         "packaging": {
@@ -870,11 +878,11 @@
         },
         "pytest": {
             "hashes": [
-                "sha256:4a784f1d4f2ef198fe9b7aef793e9fa1a3b2f84e822d9b3a64a181293a572d45",
-                "sha256:926855726d8ae8371803f7b2e6ec0a69953d9c6311fa7c3b6c1b929ff92d27da"
+                "sha256:65e92898fb5b61d0a1d7319c3e6dcf97e599e331cfdc2b27f20c0d87ece19239",
+                "sha256:9ea149066f566c943d3122f4b1cf1b577cab73189d11f490b54703fa5fa9df50"
             ],
             "index": "pypi",
-            "version": "==4.6.3"
+            "version": "==4.6.7"
         },
         "pytest-cov": {
             "hashes": [