Update regex for `RecordNotUnique` exception

Fixes issue #256

`TinyTds::Error: Violation of UNIQUE KEY constraint '<constraint_name>'. Cannot insert duplicate key in object ...` does not match the regex for `RecordNotUnique` exception.

Signed-off-by: Paula Bianca Torre <paula.torre@teamcodeflux.com>
Merge pull request #257 from codeflux/match-tiny-tds-record-not-unique-error-message

Update regex for `RecordNotUnique` exception