Commit before calling SQLDisconnect to avoid HY010 error

[h-serizawa]

"SQLDisconnect() failed with error code HY010" error happens. The cause is commit or rollback is not called before calling SQLDisconnect. Add the call of SQLEndTran(SQL_COMMIT) before SQLDisconnect in destroy method.
Close #66.

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[h-serizawa]

I committed with the wrong user info. Will re-commit later.