Fix polarity of Token.is_oov and Lexeme.is_oov (#5634)

Fix `Token.is_oov` and `Lexeme.is_oov` so they return `True` when the
lexeme does **not** have a vector.

spacy/lexeme.pyx

@@ -349,7 +349,7 @@ cdef class Lexeme:
     @property
     def is_oov(self):
         """RETURNS (bool): Whether the lexeme is out-of-vocabulary."""
-        return self.orth in self.vocab.vectors
+        return self.orth not in self.vocab.vectors
 
     property is_stop:
         """RETURNS (bool): Whether the lexeme is a stop word."""

spacy/tests/vocab_vectors/test_vectors.py

@@ -376,6 +376,6 @@ def test_vector_is_oov():
     data[1] = 2.0
     vocab.set_vector("cat", data[0])
     vocab.set_vector("dog", data[1])
-    assert vocab["cat"].is_oov is True
+    assert vocab["cat"].is_oov is False
-    assert vocab["dog"].is_oov is True
+    assert vocab["dog"].is_oov is False
-    assert vocab["hamster"].is_oov is False
+    assert vocab["hamster"].is_oov is True

spacy/tokens/token.pyx

@@ -923,7 +923,7 @@ cdef class Token:
     @property
     def is_oov(self):
         """RETURNS (bool): Whether the token is out-of-vocabulary."""
-        return self.c.lex.orth in self.vocab.vectors
+        return self.c.lex.orth not in self.vocab.vectors
 
     @property
     def is_stop(self):