Fix MarkupSafe case in setup.py

Most of pypi mirrors don't allow wrong package name case when installing
them using pip
example: c.pypi.python.org

I know, this is very painful
diff --git a/setup.py b/setup.py
index 72d6765..d4acf24 100644
--- a/setup.py
+++ b/setup.py
@@ -80,7 +80,7 @@
         'Topic :: Text Processing :: Markup :: HTML'
     ],
     packages=['jinja2', 'jinja2.testsuite', 'jinja2.testsuite.res'],
-    install_requires=['markupsafe'],
+    install_requires=['MarkupSafe'],
     extras_require={'i18n': ['Babel>=0.8']},
     test_suite='jinja2.testsuite.suite',
     include_package_data=True,