crypto/md5: typo in doc comment

by **nszabolcs**:

<pre>in the file src/pkg/crypto/md5/md5.go
-// New returns a hash.Hash computing the SHA1 checksum.
+// New returns a hash.Hash computing the MD5 checksum.


by the way the wording in the sha1 package is
// New returns a new hash.Hash computing the SHA1 checksum.
in case you want it to be consistent</pre>
