FIX: invoke==1.4.1 (pinned) pip requirement

* Causes problems for Python >= 3.8 due to bundled YAML
  RELATED TO: collections.Hashable (DEPRECATED)
* Use invoke >= 1.7.0 (that fixes the problem)

SEE:

* https://www.pyinvoke.org/changelog.html
* yaml/pyyaml#202

setup.py

@@ -125,9 +125,10 @@ def find_packages_by_root_package(where):
             "PyHamcrest <  2.0;   python_version <  '3.0'",
             "pytest-cov",
             "tox",
-            "invoke >= 1.4.0",
-            # -- HINT: path.py => path (python-install-package was renamed for python3)
-            "path >= 13.1.0;    python_version >= '3.5'",
+            "invoke >=1.7.0,<2.0; python_version <  '3.6",
+            "invoke >=1.7.0;      python_version >= '3.6'",
+            # -- HINT, was RENAMED: path.py => path (for python3)
+            "path    >= 13.1.0; python_version >= '3.5'",
             "path.py >= 11.5.0; python_version <  '3.5'",
             "pycmd",
             "pathlib; python_version <= '3.4'",

tasks/py.requirements.txt

@@ -8,12 +8,13 @@
 #  * http://www.pip-installer.org/
 # ============================================================================
 
-invoke==1.4.1
+invoke >=1.7.0,<2.0; python_version <  '3.6'
+invoke >=1.7.0;      python_version >= '3.6'
 pycmd
-six==1.15.0
+six >= 1.15.0
 
-# -- HINT: path.py => path (python-install-package was renamed for python3)
-path >= 13.1.0;    python_version >= '3.5'
+# -- HINT, was RENAMED: path.py => path (for python3)
+path    >= 13.1.0; python_version >= '3.5'
 path.py >= 11.5.0; python_version <  '3.5'
 
 # -- PYTHON2 BACKPORTS: