cargo audit reported vulnerabilities in 2.12.0

http-types 2.12.0 is the latest version. The default features pull in dependencies with reported vulnerabilities.

Steps to reproduce. The `cargo check` will create the `Cargo.lock` that `cargo audit` uses.
```
git checkout tags/v2.12.0
cargo check
cargo audit
```

```
PS C:\Users\cataggar\io\http-types> cargo audit
Fetching advisory database from `https://github.com/RustSec/advisory-db.git`
Loaded 421 security advisories (from C:\Users\cataggar\.cargo\advisory-db)
Updating crates.io index
Scanning Cargo.lock for vulnerabilities (135 crate dependencies)
Crate: aes-soft
Version: 0.6.4
Warning: unmaintained
Title: `aes-soft` has been merged into the `aes` crate
Date: 2021-04-29
ID: RUSTSEC-2021-0060
URL: https://rustsec.org/advisories/RUSTSEC-2021-0060
Dependency tree:
aes-soft 0.6.4
└── aes 0.6.0
└── aes-gcm 0.8.0
└── cookie 0.14.4
└── http-types 2.12.0

Crate: aesni
Version: 0.10.0
Warning: unmaintained
Title: `aesni` has been merged into the `aes` crate
Date: 2021-04-29
ID: RUSTSEC-2021-0059
URL: https://rustsec.org/advisories/RUSTSEC-2021-0059
Dependency tree:
aesni 0.10.0
└── aes 0.6.0
└── aes-gcm 0.8.0
└── cookie 0.14.4
└── http-types 2.12.0

Crate: cpuid-bool
Version: 0.2.0
Warning: unmaintained
Title: `cpuid-bool` has been renamed to `cpufeatures`
Date: 2021-05-06
ID: RUSTSEC-2021-0064
URL: https://rustsec.org/advisories/RUSTSEC-2021-0064
Dependency tree:
cpuid-bool 0.2.0
└── polyval 0.4.5
└── ghash 0.3.1
└── aes-gcm 0.8.0
└── cookie 0.14.4
└── http-types 2.12.0

Crate: stdweb
Version: 0.4.20
Warning: unmaintained
Title: stdweb is unmaintained
Date: 2020-05-04
ID: RUSTSEC-2020-0056
URL: https://rustsec.org/advisories/RUSTSEC-2020-0056
Dependency tree:
stdweb 0.4.20
└── time 0.2.27
└── cookie 0.14.4
└── http-types 2.12.0

warning: 4 allowed warnings found
```