[Python] Typo in ORC writer docstring: LZ0 should be LZO

[maupatel]

In python/pyarrow/orc.py, the compression parameter docstring for the ORC writer reads:

Note that LZ0 is currently not supported.

This should be LZO (Lempel-Ziv-Oberhumer). The current text uses the digit zero (LZ0), which is not a real codec name; LZO is the compression algorithm ORC references. The valid-values list just above it spells the other codecs correctly.

Minor documentation fix; I will open a PR.