Add python version requirement on setup.py

include python_requires option on setup for pip to resolve python dependency accordingly.
prevent installing the latest flask_restx regardless of python version.
fixes python-restx#586

CHANGELOG.rst

@@ -25,6 +25,18 @@ Releases prior to 0.3.0 were “best effort” filled out, but are missing
 some info. If you see your contribution missing info, please open a PR
 on the Changelog!
 
+.. _section-1.3.1:
+1.3.1
+-----
+.. _bug_fixes-1.3.1
+Bug Fixes
+~~~~~~~~~
+
+::
+
+   * Add python version requirement on setup.py (#586) [jason-the-j]
+
+
 .. _section-1.3.0:
 1.3.0
 -----

setup.py

@@ -111,4 +111,5 @@ def pip(filename):
         "Topic :: Software Development :: Libraries :: Python Modules",
         "License :: OSI Approved :: BSD License",
     ],
+    python_requires=">=3.8"
 )