Update minio/sha256-simd to a version that supports s390x.
diff -Nru a/vendor/manifest b/vendor/manifest
--- a/vendor/manifest   2017-04-15 07:38:23.000000000 +0000
+++ b/vendor/manifest   2017-05-12 20:14:19.175873879 +0000
@@ -313,7 +313,7 @@
 			"importpath": "github.com/minio/sha256-simd",
 			"repository": "https://github.com/minio/sha256-simd",
 			"vcs": "git",
-			"revision": "6124d070eb4e7001c244b6ccc282620a5dce44a0",
+			"revision": "f3ec2e4d36d43c3a899ed4b7d9f62188edcf5afd",
 			"branch": "master",
 			"notests": true
 		},