Flush ObjectOutputStream before calling toByteArray on underlying ByteArrayOutputStream

[emopers]

When an ObjectOutputStream instance wraps an underlying ByteArrayOutputStream instance, it is recommended to flush or close the ObjectOutputStream before invoking the underlying instances's toByteArray(). This pull request adds a call to the flush method before calls to the toByteArray method.

[coveralls]

Coverage remained the same at 90.17% when pulling 771772a0f455cbdc6f0cce66bff8767e2522731c on emopers:bug_fix into d7d4e4df72cc14998ff82a936e8a8de10931e5af on apache:master.