FIX: pytest-html v4.0.0 causes pytest run to fail

* UPDATE: Some dependencies, too.

Author: jenisys

py.requirements/basic.txt

@@ -7,7 +7,7 @@
 # ============================================================================
 
 click >= 6.6
-six >= 1.12
+six >= 1.15
 
 # -- USE BACKPORT: For Python2 and some Python3
 # IMPROVED: configparser from Python 3.5

py.requirements/develop.txt

@@ -23,7 +23,7 @@ bump2version >= 0.5.6
 twine
 
 # -- TEST/DEVELOP SUPPORT:
-tox >= 1.8
+tox >= 1.8,<4.0     # HINT: tox >= 4.0 changes/breaks some things.
 coverage>=4.2
 -r testing.txt
 

py.requirements/testing.txt

@@ -10,7 +10,9 @@
 # -- TEST SUPPORT:
 pytest <  5.0; python_version <  '3.0'  # >= 4.2
 pytest >= 5.0; python_version >= '3.0'
-pytest-html >= 1.19.0
+
+pytest-html >= 1.19.0,<2.0; python_version <  '3.0'
+pytest-html >= 2.0,<4.0;    python_version >= '3.0'
 
 # -- USE: click.testing
 click >= 6.6

setup.py

@@ -115,13 +115,14 @@ def make_long_description(marker=None, intro=None):
     python_requires=">=2.7, !=3.0.*, !=3.1.*",
     install_requires=[
         "click >= 6.6",
-        "six >= 1.10",
+        "six >= 1.15",
         "configparser >= 3.5.0; python_version < '3.5'",
     ],
     tests_require=[
         "pytest <  5.0; python_version <  '3.0'", # >= 4.2
         "pytest >= 5.0; python_version >= '3.0'",
-        "pytest-html >= 1.19.0",
+        "pytest-html >= 1.19.0,<2.0; python_version <  '3.0'",
+        "pytest-html >= 2.0,<4.0;    python_version >= '3.0'",
     ],
 #     extras_require={
 #         # -- SUPPORT-WHEELS: Extra packages for Python2.6 and ...