Updates version number to 0.4.172763892.20171019.
Updates version number to 0.4.172763892.20171019.

Significant changes:
- Change PBXProject last upgrade check to Xcode 9.
- Fixed an issue with dSYM not being processed for
  extensions/frameworks of a target.

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PiperOrigin-RevId: 172774481
MOS_MIGRATED_REVID=172774481

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