fix parsing

some lines have a space " " as a token, like
```
O
```

pico-breast-cancer.py

@@ -153,9 +153,9 @@ class PicoBreastCancer(datasets.GeneratorBasedBuilder):
                         ner_tags = []
                 else:
                     # conll2003 tokens are space separated
-                    splits = line.split(" ")
+                    splits = line.rstrip().rsplit(" ", 1)
                     tokens.append(splits[0])
-                    ner_tags.append(splits[1].rstrip())
+                    ner_tags.append(splits[1])
             # last example
             if tokens:
                 yield idx, {