fix: replaced http for https in characters data

[KoolTheba]

Hi @KostaSav 😄

Thanks a lot for creating this api! It's helping tons of students with their pet projects.

The scenario of this PR:

• Heroku provides you already a SSL certificate, so you can return the images url in the characters payload with https protocol. That way Frontend apps that consume your api, won't face any mixed-content issues when deploying the project under https, like GitHub pages, etc

Main change

• Updated protocol for the images url in the payload

Changelog

• 55e4511 fix: replaced http for https in characters data by @KoolTheba

[KostaSav]

Thank you @KoolTheba for contributing with this significant change!