blake2b: fix comments in grammar

Change-Id: Idacdbf5ee847be6e21ecce0c9d41818e643c4835
GitHub-Last-Rev: bf1a719b62167d294319f23576302ef567894cc3
GitHub-Pull-Request: golang/crypto#73
Reviewed-on: https://go-review.googlesource.com/c/158837
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

blake2b/blake2b.go

@@ -75,19 +75,19 @@ func Sum256(data []byte) [Size256]byte {
 }
 
 // New512 returns a new hash.Hash computing the BLAKE2b-512 checksum. A non-nil
-// key turns the hash into a MAC. The key must between zero and 64 bytes long.
+// key turns the hash into a MAC. The key must be between zero and 64 bytes long.
 func New512(key []byte) (hash.Hash, error) { return newDigest(Size, key) }
 
 // New384 returns a new hash.Hash computing the BLAKE2b-384 checksum. A non-nil
-// key turns the hash into a MAC. The key must between zero and 64 bytes long.
+// key turns the hash into a MAC. The key must be between zero and 64 bytes long.
 func New384(key []byte) (hash.Hash, error) { return newDigest(Size384, key) }
 
 // New256 returns a new hash.Hash computing the BLAKE2b-256 checksum. A non-nil
-// key turns the hash into a MAC. The key must between zero and 64 bytes long.
+// key turns the hash into a MAC. The key must be between zero and 64 bytes long.
 func New256(key []byte) (hash.Hash, error) { return newDigest(Size256, key) }
 
 // New returns a new hash.Hash computing the BLAKE2b checksum with a custom length.
-// A non-nil key turns the hash into a MAC. The key must between zero and 64 bytes long.
+// A non-nil key turns the hash into a MAC. The key must be between zero and 64 bytes long.
 // The hash size can be a value between 1 and 64 but it is highly recommended to use
 // values equal or greater than:
 // - 32 if BLAKE2b is used as a hash function (The key is zero bytes long).