Incorrect URL redirection in the doc of BTreeMap

[luojia65]

When I open the doc for std::collections::btree_map::BTreeMap, I found a hyperlink referring to BTreeMap on the second line, which incorrectly redirect to:

https://doc.rust-lang.org/std/collections/btree_set/struct.BTreeMap.html

instead of one of the following:

https://doc.rust-lang.org/std/collections/btree_map/struct.BTreeMap.html
https://doc.rust-lang.org/std/collections/struct.BTreeMap.html

thus caused an HTTP 404 error.

Looking into the source code, I found out that this hyperlink redirects to struct.BTreeMap.html. This could work for the type aliases of BTreeSet as std::collections::BTreeSet, for the reason that struct.BTreeSet.html and struct.BTreeMap.html are together in the same path, but does not work for std::collections::btree_set::BTreeSet as there isn't a BTreeMap in std::collections::btree_set.

Additionally, there is also an incorrect redirection on std::colletions::hash_set::HashSet where there is a hyperlink for struct HashMap which does not exist in std::collections::hash_set.

The rust version for doc.rust-lang.org is Version 1.28.0 (9634041f0 2018-07-30).

[ollie27]

This is a duplicate of #32130.

[luojia65]

(Closing this because of duplication)