dev env: add upper version constraint for importlib-metadata to keep compatibility with python3.5

https://github.com/fphammerle/ical2vdir/commit/79ba44e313c5b16df3c4fe150a21ceab72b45403

Pipfile

@@ -25,6 +25,8 @@ pylint-import-requirements = "*"
 pytest-cov = "*"
 
 # python3.5 compatibility
+# https://github.com/python/importlib_metadata/commit/107f9029fd5807c6579b881db19e11a0488f0675
+importlib-metadata = "<3"
 isort = "<5"
 # workaround https://github.com/pytest-dev/pytest/issues/3953
 pathlib2 = {version = "*", markers="python_version < '3.6'"}

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "808a521362576e0c9b9250ff98dc4749714e543afbe5502e54617ccf28e61791"
+            "sha256": "ae1a73458f915e342844bad163ab1657b3a5e41bbb70d7556d72a2d561cd4fda"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -109,6 +109,7 @@
                 "sha256:77a540690e24b0305878c37ffd421785a6f7e53c8b5720d211b211de8d0e95da",
                 "sha256:cefa1a2f919b866c5beb7c9f7b0ebb4061f30a8a9bf16d609b000e2dfaceb9c3"
             ],
+            "index": "pypi",
             "version": "==2.0.0"
         },
         "iniconfig": {