test env: added library stubs for pyyaml to prepare mypy upgrade from v0.812 to v0.902

Pipfile

@@ -19,6 +19,7 @@ mypy = "*"
 pylint-import-requirements = "*"
 #pytest = "*"
 pytest-cov = "*"
+types-PyYAML = "<5.4"
 
 # python3.5 compatibility
 # https://github.com/PyCQA/astroid/commit/d81f07becf3243a84e0baaa3493ce74cafed8022#diff-60f61ab7a8d1910d86d9fda2261620314edcae5894d5aaa236b821c7256badd7R52

Pipfile.lock

@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "d81240934f3dd4a1b8eddd5a052fd45471c1c67e408a69714fab736a837a94c2"
+            "sha256": "bd1fef1034ac9bf1dc6d35243c6750e8053c003dfcee1fe71420a2960ab24c62"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -398,6 +398,13 @@
             ],
             "version": "==1.4.3"
         },
+        "types-pyyaml": {
+            "hashes": [
+                "sha256:0ad719fa27fb97ee0aef7866ae90f80aaba226a7e6b900b3e1eb562a85c0e4da"
+            ],
+            "index": "pypi",
+            "version": "==0.1.9"
+        },
         "typing-extensions": {
             "hashes": [
                 "sha256:0ac0f89795dd19de6b97debb0c6af1c70987fd80a2d62d1958f7e56fcc31b497",