Change license to SPDX identifier

Author: kovidgoyal

setup.cfg

@@ -4,10 +4,10 @@ version = 0.4.12
 author = Kovid Goyal
 author_email = [email protected]
 description = Fast C based HTML 5 parsing for python
-license = Apache 2.0
+license = Apache-2.0
 url = https://html5-parser.readthedocs.io
 platforms = any
-classifiers = 
+classifiers =
     Development Status :: 5 - Production/Stable
     Intended Audience :: Developers
     License :: OSI Approved :: Apache Software License
@@ -23,7 +23,7 @@ classifiers =
 package_dir =
    =src
 packages = html5_parser
-install_requires = 
+install_requires =
     chardet
     lxml>=3.8.0