Fix for new unique constraint message of SQLite 3.8.2 in test

SQLite 3.8.2 changed its error messages format for unique constrains and now our tests in Fedora fails. This fixes the issue.
```
+ testrb -Ilib test/test_backup.rb test/test_collation.rb test/test_database.rb test/test_database_readonly.rb test/test_deprecated.rb test/test_encoding.rb test/test_integration.rb test/test_integration_open_close.rb test/test_integration_pending.rb test/test_integration_resultset.rb test/test_integration_statement.rb test/test_result_set.rb test/test_sqlite3.rb test/test_statement.rb test/test_statement_execute.rb
Run options: -Ilib
# Running tests:
.......................................................................................F........................................................................................S..................................................
Finished tests in 3.438005s, 66.0267 tests/s, 108.7840 assertions/s.
  1) Failure:
SQLite3::TestStatement#test_insert_duplicate_records [/builddir/build/BUILD/sqlite3-1.3.8/usr/share/gems/gems/sqlite3-1.3.8/test/test_statement.rb:33]:
Expected /column(s)? .* (is|are) not unique/ to match "UNIQUE constraint failed: things.name".
227 tests, 374 assertions, 1 failures, 0 errors, 1 skips
```
This fixes https://github.com/sparklemotion/sqlite3-ruby/issues/116