Fix setup.py typo

Author: ArrowAcrobatics

setup.py

@@ -14,7 +14,7 @@
     packages=find_packages(exclude=['examples', 'tests']),
     install_requires=list(package.strip() for package in open('requirements.txt')),
     classifiers=[
-        'Programming Language :: Python :: 3.7'
+        'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8'
     ],
     python_requires='>=3.7',