add missing identifier for 3.7

Author: skvark

setup.py

@@ -188,6 +188,7 @@ def main():
           'Programming Language :: Python :: 3.4',
           'Programming Language :: Python :: 3.5',
           'Programming Language :: Python :: 3.6',
+          'Programming Language :: Python :: 3.7',
           'Programming Language :: C++',
           'Programming Language :: Python :: Implementation :: CPython',
           'Topic :: Scientific/Engineering',