node v6 bugfix: don't convert NodeBuffer to Uint8Array

lib/csr.js

@@ -110,13 +110,13 @@ RSA.sign = function signRsa(keypem, ab) {
   return Promise.resolve().then(function () {
     // Signer is a stream
     var sign = crypto.createSign('SHA256');
-    sign.write(new Uint8Array(ab));
+    sign.write(ab);
     sign.end();
 
     // The signature is ASN1 encoded, as it turns out
     var sig = sign.sign(keypem);
 
     // Convert to a JavaScript ArrayBuffer just because
-    return new Uint8Array(sig.buffer.slice(sig.byteOffset, sig.byteOffset + sig.byteLength));
+    return sig.buffer.slice(sig.byteOffset, sig.byteOffset + sig.byteLength);
   });
 };