env: downgrade pylint to restore compatibility with python3.4

https://travis-ci.org/fphammerle/free-disk/jobs/630907704#L198

Pipfile

@@ -9,7 +9,9 @@ free-disk = {editable = true, path = "."}
 [dev-packages]
 # v8.0.0 dropped python3.4 support
 more-itertools = "<8"
-pylint = ">=2.3.0"
+# v2.4.0 dropped python3.4 support
+# https://github.com/PyCQA/pylint/commit/927db96bbd343a61428faa0249fdeec58cfb3ebe
+pylint = ">=2.3.0,<2.4.0"
 # v5.0.0 dropped python3.4. support
 # https://github.com/pytest-dev/pytest/commit/4d49ba65297102110ae8aeecdb3b82b23a231fba
 pytest = "<5"

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "ce6f5a3c2c9d7747263810d63aa755c49351f4a973e7713e23db23db1648c3fe"
+            "sha256": "70a80c9b86b4ccddae08d2c528a756c9411cda321dc664fc335d245c6422b5cd"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -122,11 +122,11 @@
         },
         "pylint": {
             "hashes": [
-                "sha256:3db5468ad013380e987410a8d6956226963aed94ecb5f9d3a28acca6d9ac36cd",
-                "sha256:886e6afc935ea2590b462664b161ca9a5e40168ea99e5300935f6591ad467df4"
+                "sha256:5d77031694a5fb97ea95e828c8d10fc770a1df6eb3906067aaed42201a8a6a09",
+                "sha256:723e3db49555abaf9bf79dc474c6b9e2935ad82230b10c1138a71ea41ac0fff1"
             ],
             "index": "pypi",
-            "version": "==2.4.4"
+            "version": "==2.3.1"
         },
         "pyparsing": {
             "hashes": [