doc: correct name of engine methods

ENGINE_METHOD_PKEY_METH and ENGINE_METHOD_PKEY_ASN1_METH are misspelled
in the documentation, both should be ..._METHS.

PR-URL: https://github.com/nodejs/node/pull/5463
Reviewed-By: Fedor Indutny <fedor@indutny.com>

doc/api/crypto.markdown

@@ -1272,8 +1272,8 @@ is a bit field taking one of or a mix of the following flags (defined in the
 * `ENGINE_METHOD_CIPHERS`
 * `ENGINE_METHOD_DIGESTS`
 * `ENGINE_METHOD_STORE`
-* `ENGINE_METHOD_PKEY_METH`
-* `ENGINE_METHOD_PKEY_ASN1_METH`
+* `ENGINE_METHOD_PKEY_METHS`
+* `ENGINE_METHOD_PKEY_ASN1_METHS`
 * `ENGINE_METHOD_ALL`
 * `ENGINE_METHOD_NONE`