Change package name to 'gssapi' in setup.py

As decided, the name of the package has been changed to 'gssapi'
in setup.py.

Author: DirectXMan12

Diff for: setup.py

@@ -153,7 +153,7 @@ def gssapi_modules(lst):
                                  open('README.txt').read())))
 
 setup(
-    name='PythonGSSAPI',
+    name='gssapi',
     version='1.0.0',
     author='The Python GSSAPI Team',
     author_email='[email protected]',