added Flask, updated version

Author: dmalan

setup.py

@@ -10,11 +10,11 @@
         "Topic :: Software Development :: Libraries :: Python Modules"
     ],
     description="CS50 library for Python",
-    install_requires=["SQLAlchemy", "sqlparse", "termcolor"],
+    install_requires=["Flask", "SQLAlchemy", "sqlparse", "termcolor"],
     keywords="cs50",
     name="cs50",
     package_dir={"": "src"},
     packages=["cs50"],
     url="https://github.com/cs50/python-cs50",
-    version="2.4.1"
+    version="2.4.2"
 )