Added uninstall function to setup

bin/video2x_setup.py

@@ -89,6 +89,7 @@ class Video2xSetup:
     def _install_python_requirements(self):
         """ Read requirements.txt and return its content
         """
+        pip_uninstall('requirements.txt')
         pip_install('requirements.txt')
 
     def _cleanup(self):
@@ -209,6 +210,13 @@ def pip_install(file):
     """
     return subprocess.run([sys.executable, '-m', 'pip', 'install', '-U', '-r', file]).returncode
 
+def pip_uninstall(file):
+    """ Uninstall python package via python pip module
+    
+    pip.main() is not available after pip 9.0.1, thus
+    pip module is not used in this case.
+    """
+    return subprocess.run([sys.executable, '-m', 'pip', 'uninstall', '-r', file, '-y']).returncode
 
 if __name__ == '__main__':
     try: