remove claims of Python 3.5 support

brings `setup.py` up to sync with #2713 & #2715 changes

setup.py

@@ -207,7 +207,7 @@ def run(self):
 
 For alternative modes of installation, see the `documentation <http://radimrehurek.com/gensim/install.html>`_.
 
-Gensim is being `continuously tested <https://travis-ci.org/RaRe-Technologies/gensim>`_ under Python 3.5, 3.6, 3.7 and 3.8.
+Gensim is being `continuously tested <https://travis-ci.org/RaRe-Technologies/gensim>`_ under Python 3.6, 3.7 and 3.8.
 Support for Python 2.7 was dropped in gensim 4.0.0 – install gensim 3.8.3 if you must use Python 2.7.
 
 
@@ -375,7 +375,6 @@ def run(self):
         'Environment :: Console',
         'Intended Audience :: Science/Research',
         'Operating System :: OS Independent',
-        'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
@@ -386,7 +385,7 @@ def run(self):
     ],
 
     test_suite="gensim.test",
-    python_requires='>=3.5',
+    python_requires='>=3.6',
     setup_requires=setup_requires,
     install_requires=install_requires,
     tests_require=linux_testenv,