Use digest from the master branch

Author: newpavlov

Cargo.lock

@@ -35,4 +35,4 @@ sha1 = { path = "sha1" }
 sha3 = { path = "sha3" }
 whirlpool = { path = "whirlpool" }
 
-digest = { git = "https://github.com/RustCrypto/traits", branch = "digest/rm_rt_variable" }
+digest = { git = "https://github.com/RustCrypto/traits" }