Motivation for this change

After upgrading to NixOS 20.03, I've got the following warning:

nginx: [warn] could not build optimal types_hash, you should increase either types_hash_max_size: 2048 or types_hash_bucket_size: 64; ignoring types_hash_bucket_size

The documentation states that "if nginx emits the message requesting
to increase either hash max size or hash bucket size then the first
parameter should first be increased" (aka types_hash_max_size).

In 19.03, the size of mime.types was around 100 entries. In 20.03, we
are around 900 entries. This is due to ff0148d which makes nginx
use mailcap mime.types.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.