Allow step=1 when slicing a Doc

spacy/tokens/doc.pyx

@@ -87,7 +87,7 @@ cdef class Doc:
             token (Token):
         """
         if isinstance(i, slice):
-            if i.step is not None:
+            if not (i.step is None or i.step == 1):
                 raise ValueError("Stepped slices not supported in Span objects."
                                  "Try: list(doc)[start:stop:step] instead.")
             if i.start is None:

tests/tokens/test_tokens_api.py

@@ -16,6 +16,8 @@ def test_getitem(EN):
     assert not '/'.join(token.orth_ for token in span)
     span = tokens[1:4]
     assert '/'.join(token.orth_ for token in span) == 'it/back/!'
+    span = tokens[1:4:1]
+    assert '/'.join(token.orth_ for token in span) == 'it/back/!'
     with pytest.raises(ValueError):
         tokens[1:4:2]
     with pytest.raises(ValueError):