Use string interpolation

Author: djnalluri

common/etc/nginx/include/s3gateway.js

@@ -1049,7 +1049,7 @@ async function _fetchWebIdentityCredentials(r) {
         if (sts_regional === 'regional') {
             var region = process.env['AWS_REGION'];
             if (region) {
-                sts_endpoint = 'https://sts.' + region + '.amazonaws.com';
+                sts_endpoint = `https://sts.${region}.amazonaws.com`;
             } else {
                 throw 'Missing required AWS_REGION env variable';
             }
@@ -1060,7 +1060,7 @@ async function _fetchWebIdentityCredentials(r) {
 
     var token = fs.readFileSync(process.env['AWS_WEB_IDENTITY_TOKEN_FILE']);
 
-    var params = "Version=2011-06-15&Action=AssumeRoleWithWebIdentity&RoleArn=" + arn + "&RoleSessionName=" + name + "&WebIdentityToken=" + token;
+    var params = `Version=2011-06-15&Action=AssumeRoleWithWebIdentity&RoleArn=${arn}&RoleSessionName=${name}&WebIdentityToken=${token}`;
 
     var response = await ngx.fetch(sts_endpoint + "?" + params, {
         headers: {