Update classifiers

Author: utf

setup.py

@@ -61,7 +61,7 @@
             "phonons": ["phonopy>=1.10.8"],
         },
         classifiers=[
-            "programming language :: python :: 3",
+            "Programming Language :: Python :: 3",
             "Programming Language :: Python :: 3.7",
             "Programming Language :: Python :: 3.8",
             "Programming Language :: Python :: 3.9",