Change license identifier to Zlib (#279)

Author: Zuzu-Typ

setup.cfg

@@ -8,7 +8,7 @@ long_description = file: README.md
 long_description_content_type = text/markdown
 keywords = GLM, OpenGL, matrix, vector, vec, mat, Mathematics, 3D, python, python3, 3, library, python-c-api, c-api, math-library, numpy, pyrr, pip, pypi, matrix-manipulation, matrix-multiplication, matrix-functions, quaternion, c, glsl
 python_requires = >=3.7
-license = zlib/libpng license
+license = Zlib
 classifiers =
     Development Status :: 5 - Production/Stable
     Intended Audience :: Developers