setup: Update install_requires

* Remove WebError (not needed)
* Make ArgParse dependent on interpreter version

setup.py

@@ -1,3 +1,4 @@
+import sys
 try:
     from setuptools import setup, find_packages
 except ImportError:
@@ -5,6 +6,13 @@ except ImportError:
     distribute_setup.use_setuptools()
     from setuptools import setup, find_packages
 
+install_requires = [
+    'WebOb',
+]
+
+if sys.version_info < (2, 7):
+    install_requires.append('ArgParse')
+
 setup(
     name='Milla',
     version='0.1.1',
@@ -12,11 +20,7 @@ setup(
     author='Dustin C. Hatch',
     author_email='admiralnemo@gmail.com',
     url='', #TODO: Bitbucket URL here
-    install_requires=[
-        'WebOb',
-        'WebError',
-        'ArgParse',
-    ],
+    install_requires=install_requires,
     packages=find_packages('src', exclude=['distribute_setup']),
     package_dir={'': 'src'},
     entry_points={