typo in hmac comment

R=r
DELTA=1  (0 added, 0 deleted, 1 changed)
OCL=29307
CL=29307

src/lib/crypto/hmac/hmac.go

@@ -4,7 +4,7 @@
 
 // The hmac package implements the Keyed-Hash Message Authentication Code (HMAC)
 // as defined in U.S. Federal Information Processing Standards Publication 198.
-// An HMAC is a cryptographic hash attesting that uses a key to sign a message.
+// An HMAC is a cryptographic hash that uses a key to sign a message.
 // The receiver verifies the hash by recomputing it using the same key.
 package hmac