Fixed typo in gem name.

Should be discontinue, not distcontinue.  Also, update the gem file so that the bundle install runs and the tests work correctly.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>
Add product functionality and tests for is sold and discontinued functionality.

All test are passing.

Signed-off-by: Nathan Lowrie <nate@finelineautomation.com>