Make importlib dependency conditional on the Python version.

setup.py

@@ -15,10 +15,13 @@ def get_version():
     raise RuntimeError('No version info found.')
 
 def get_dependencies():
-    deps = ['redis', 'procname', 'importlib', 'times']
+    deps = ['redis', 'procname', 'times']
     deps += ['logbook']  # should be soft dependency?
     if sys.version_info < (2, 7) or \
-       sys.version_info >= (3, 0) and sys.version_info < (3, 2):
+            (sys.version_info >= (3, 0) and sys.version_info < (3, 1)):
+        deps += ['importlib']
+    if sys.version_info < (2, 7) or \
+            (sys.version_info >= (3, 0) and sys.version_info < (3, 2)):
         deps += ['argparse']
     return deps