add missing comma

Author: mr-c

setup.py

@@ -99,7 +99,7 @@
           'Programming Language :: Python :: 3.4',
           'Programming Language :: Python :: 3.5',
           'Programming Language :: Python :: 3.6',
-          "Programming Language :: Python :: 3.7"
+          'Programming Language :: Python :: 3.7',
           'Topic :: Scientific/Engineering',
           'Topic :: Scientific/Engineering :: Bio-Informatics',
           'Topic :: Scientific/Engineering :: Astronomy',