Update dependencies

Among others, this updates minio-go, so that the new "eu-west-3" zone
for AWS is supported.

vendor/golang.org/x/sys/unix/env_unix.go

@@ -25,3 +25,7 @@ func Clearenv() {
 func Environ() []string {
 	return syscall.Environ()
 }
+
+func Unsetenv(key string) error {
+	return syscall.Unsetenv(key)
+}