env: downgrade pytest to restore compatibility with python3.4

https://travis-ci.org/fphammerle/free-disk/jobs/630906241#L211

Pipfile

@@ -10,7 +10,9 @@ free-disk = {editable = true, path = "."}
 # v8.0.0 dropped python3.4 support
 more-itertools = "<8"
 pylint = ">=2.3.0"
-pytest = "*"
+# v5.0.0 dropped python3.4. support
+# https://github.com/pytest-dev/pytest/commit/4d49ba65297102110ae8aeecdb3b82b23a231fba
+pytest = "<5"
 
 [requires]
 python_version = "3"

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "d4b79fc22599a54a52c244bea5819bc07a905d093eb2d6032a3b35042fe0fce4"
+            "sha256": "ce6f5a3c2c9d7747263810d63aa755c49351f4a973e7713e23db23db1648c3fe"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -29,6 +29,13 @@
             ],
             "version": "==2.3.3"
         },
+        "atomicwrites": {
+            "hashes": [
+                "sha256:03472c30eb2c5d1ba9227e4c2ca66ab8287fbfbbda3888aa93dc2e28fc6811b4",
+                "sha256:75a9445bac02d8d058d5e1fe689654ba5a6556a1dfd8ce6ec55a0ed79866cfa6"
+            ],
+            "version": "==1.3.0"
+        },
         "attrs": {
             "hashes": [
                 "sha256:08a96c641c3a74e44eb59afb61a24f2cb9f4d7188748e76ba4bb5edfa3cb7d1c",
@@ -130,11 +137,11 @@
         },
         "pytest": {
             "hashes": [
-                "sha256:6b571215b5a790f9b41f19f3531c53a45cf6bb8ef2988bc1ff9afb38270b25fa",
-                "sha256:e41d489ff43948babd0fad7ad5e49b8735d5d55e26628a58673c39ff61d95de4"
+                "sha256:6192875be8af57b694b7c4904e909680102befcb99e610ef3d9f786952f795aa",
+                "sha256:f8447ebf8fd3d362868a5d3f43a9df786dfdfe9608843bd9002a2d47a104808f"
             ],
             "index": "pypi",
-            "version": "==5.3.2"
+            "version": "==4.6.8"
         },
         "six": {
             "hashes": [