only set S3 endpoint if it's defined

lib/transports/s3/remote.js

@@ -3,10 +3,11 @@ var AWS = require("aws-sdk"),
 
 module.exports = function(bucket, storagePath) {
 
-  var s3 = new AWS.S3({
-    params: { Bucket: bucket },
-    endpoint: process.env.S3_ENDPOINT || 's3.amazonaws.com'
-  });
+  var s3Options = { params: { Bucket: bucket } };
+  if (process.env.S3_ENDPOINT) {
+    S3Options.endpoint = process.env.S3_ENDPOINT;
+  }
+  var s3 = new AWS.S3(s3Options);
 
   // Test credentials
   s3.headBucket({}, function(err){ if (err) { throw err; } });