Fixed metadata bug in the build file

Author: OwenCochell

pyproject.toml

@@ -31,7 +31,7 @@ classifiers = [
   "Topic :: Software Development :: Libraries",
   "License :: OSI Approved :: MIT License",
   "Programming Language :: Python :: 3 :: Only",
-  "Programming Language :: Python :: 3.6 :: Only",
+  "Programming Language :: Python :: 3.6",
   "Programming Language :: Python :: 3.7",
   "Programming Language :: Python :: 3.8",
   "Programming Language :: Python :: 3.9",