Dynamic keys are ignored due to the asterisk at the end of the key

`match_to_key` adds asterisk (`*`) to the dynamic keys, thus making the key invalid and `valid_key?` to return false. And because of that, next is called and all the dynamic keys are skipped.

This fix removes the line that adds the asterisk from `match_to_key` and adds it after the `valid_key?` is called. In addition, instead of adding asterisk at the end of the key, colon (`:`) is added. This is inline with the commit "stricter dynamic key match" https://github.com/glebm/i18n-tasks/commit/ee6c5728a0ef94a6ae056da318fe788cd198c208