Build error: in compatibility with hmac change

[stevenhorsman]

The Cargo.toml states that it supports hmac ">=0.11", but it is using the NewMac trait that has been removed in v0.12.0.

This results in the error:

error[E0432]: unresolved import `hmac::NewMac`
 --> src/blockcipher/aes_ctr.rs:8:23
  |
8 | use hmac::{Hmac, Mac, NewMac};
  |                       ^^^^^^ no `NewMac` in the root

error[E0308]: mismatched types
  --> src/blockcipher/aes_ctr.rs:54:41
   |
54 |                     hmac.clone().verify(&self.exp_hmac).map_err(|_| {
   |                                         ^^^^^^^^^^^^^^ expected struct `GenericArray`, found struct `Vec`
   |
   = note: expected reference `&GenericArray<u8, UInt<UInt<UInt<UInt<UInt<UInt<UTerm, B1>, B0>, B0>, B0>, B0>, B0>>`
              found reference `&Vec<u8>`

Some errors have detailed explanations: E0308, E0432.
For more information about an error, try `rustc --explain E0308`.
error: could not compile `ocicrypt-rs` due to 2 previous errors

when running cargo build --all-features

Whether the trait should have been removed from a version change 0.11 to 0.12 is another issue, but in the mean time it would be good to fix up the build here.