Remove superflous string quotes

Author: nblock

vdirsyncer/storage/memory.py

@@ -18,7 +18,7 @@ class MemoryStorage(Storage):
 
     def __init__(self, fileext="", **kwargs):
         if kwargs.get("collection") is not None:
-            raise exceptions.UserError("MemoryStorage does not support " "collections.")
+            raise exceptions.UserError("MemoryStorage does not support collections.")
         self.items = {}  # href => (etag, item)
         self.metadata = {}
         self.fileext = fileext