LRU cache throws KeyError on add()

[MrCreosote]

Might be fixed by 937d2df, but thought I'd report just in case. Follow on issue from #4.

In [1]: import cacheout

In [2]: c = cacheout.LRUCache()

In [3]: c.add('foo', 'bar')
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-3-09536a570d71> in <module>()
----> 1 c.add('foo', 'bar')

~/anaconda3/lib/python3.6/site-packages/cacheout/cache.py in add(self, key, value, ttl)
    271         """
    272         with self._lock:
--> 273             self._add(key, value, ttl=ttl)
    274 
    275     def _add(self, key, value, ttl=None):

~/anaconda3/lib/python3.6/site-packages/cacheout/cache.py in _add(self, key, value, ttl)
    274 
    275     def _add(self, key, value, ttl=None):
--> 276         if self._has(key):
    277             return
    278         self._set(key, value, ttl=ttl)

~/anaconda3/lib/python3.6/site-packages/cacheout/cache.py in _has(self, key)
    181     def _has(self, key):
    182         # Use get method since it will take care of evicting expired keys.
--> 183         return self._get(key, default=_NOTSET) is not _NOTSET
    184 
    185     def size(self):

~/anaconda3/lib/python3.6/site-packages/cacheout/lru.py in _get(self, key, default)
     14     def _get(self, key, default=None):
     15         value = super()._get(key, default=default)
---> 16         self._cache.move_to_end(key)
     17         return value

KeyError: 'foo'

[MrCreosote]

Confirmed fixed in 0.10.2