examples: fix env for python3.6

.github/workflows/python.yml

@@ -136,7 +136,7 @@ jobs:
       matrix:
         python-version:
         #- 3.5 TODO
-        #- 3.6 TODO
+        - 3.6
         - 3.7
         #- 3.8 TODO
         #- 3.9 TODO

examples/Pipfile

@@ -10,5 +10,11 @@ matplotlib = "*"
 seaborn = "*"
 notebook = "*"
 
+# workaround pipenv expectedly adding "python_version >= '3.7'" marker:
+# >  File "/home/runner/.local/share/virtualenvs/examples-bH_l4rXc/lib/python3.5/site-packages/nbconvert/exporters/base.py", line 10, in <module>
+# >    from traitlets.log import get_logger
+# >ImportError: No module named 'traitlets'
+traitlets = "*"
+
 [requires]
 python_version = "3"

examples/Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "f850f4eed129655a3b966819d613859c207e68aafecac0405046d4f31ccfc144"
+            "sha256": "a31c31d2e17374347a7f81dfc6c2c31d0212346029910111806ed42c18a0d0de"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -684,7 +684,7 @@
                 "sha256:70b4c6a1d9019d7b4f6846832288f86998aa3b9207c6821f3578a6a6a467fe44",
                 "sha256:d023ee369ddd2763310e4c3eae1ff649689440d4ae59d7485eb4cfbbe3e359f7"
             ],
-            "markers": "python_version >= '3.7'",
+            "index": "pypi",
             "version": "==4.3.3"
         },
         "wcwidth": {