fix: corner case in prototype of VersionMappings

Note the 'not' placement; every repo derived from
this already does overriding so this has never
shown, but this effectively has been checking if a
boolean was there, instead of the actual key.

Signed-off-by: Brian Harring <ferringb@gmail.com>

Author: ferringb

src/pkgcore/repository/prototype.py

@@ -76,7 +76,7 @@ def __getitem__(self, key):
         o = self._cache.get(key)
         if o is not None:
             return o
-        if not key[1] in self._parent.get(key[0], ()):
+        if key[1] not in self._parent.get(key[0], ()):
             raise KeyError(key)
         val = tuple(self._pull_vals(key))
         self._cache[key] = val