Changed the protocol of the URL used as a custom search engine from `http` to `https`.
The reason for this change is that `www.stackage.org` only uses `https`,
so every time the custom search engine is used,
a redirect from `http` to `https` occurs,
sacrificing the cleanliness of the history.
On `www.stackage.org`,
the HTTP header is set to
`strict-transport-security max-age=15724800; includeSubDomains` for HSTS,
so there's no need to try connecting via http.
This is a bit unclear to me as well,
but even though HSTS is set and a redirect is set for subsequent access,
it seems that no communication is being made,
but it is left in the history.
In any case,
I think it's wasteful to constantly access http when it's specialized for https to the point of setting HSTS,
so I'm making this commit.
