Fix aiohttp version to be compatible with Python 3.7

setup.py

@@ -36,7 +36,7 @@
     url="https://github.com/VirusTotal/vt-py",
     packages=["vt"],
     python_requires=">=3.7.0",
-    install_requires=["aiohttp"],
+    install_requires=["aiohttp==3.8.6"],
     setup_requires=["pytest-runner"],
     extras_require={"test": ["pytest", "pytest_httpserver", "pytest_asyncio"]},
     classifiers=[