build: prevent incompatible pycares versions (#215)

Author: truenicoco

setup.py

@@ -21,7 +21,7 @@ def get_version():
     license='MIT',
     long_description=codecs.open('README.rst', encoding='utf-8').read(),
     long_description_content_type='text/x-rst',
-    install_requires=['pycares>=4.9.0'],
+    install_requires=['pycares>=4.9.0,<5'],
     packages=['aiodns'],
     package_data={'aiodns': ['py.typed']},
     platforms=['POSIX', 'Microsoft Windows'],