Updates version number to 0.4.231786878.20190131.
Updates version number to 0.4.231786878.20190131.

Significant changes:

PiperOrigin-RevId: 231793296

pinterest/tulsi,pinterest/tulsi,bazelbuild/tulsi,pinterest/tulsi,pinterest/tulsi,bazelbuild/tulsi,pinterest/tulsi,pinterest/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi,bazelbuild/tulsi