[platform-common] advance sonic-platform-common submodule head (#2339)

- Merge pull request #18 from yxieca/no_buffering
- Revert "Pep 8 compliance, code cleanup (#15)" (#16)
- Pep 8 compliance, code cleanup (#15)
- add detailed comments for get_transceiver_change_event (#12)


Signed-off-by: Ying Xie <ying.xie@microsoft.com>