Resolve validation.go panic

[aymanapatel]

Branch Affected

epsiode_7

Reference to Issue

Fixes #20: Valid request throws error: Interface conversion error is nil not validator.validationerrors for valid request body

[zigmd]

So delete wasn't covered in the series.

If you're transitioning from episode 6 to episode 7, do the following:-

1. Implement get single product
2. Implement delete (raised a PR as the one in this branch doesn't work)
3. Reduce boilerplate code from (get single product, update, and delete handler functions which convert string ID to integer ID). This is present in the function findProductID in the products handler.
4. Use only the validate.go fix provided by @aymanapatel