Refactor for readability

lib/sequelize.js

@@ -979,19 +979,18 @@ class Sequelize {
     if (!autoCallback) return transaction.prepareEnvironment().return(transaction);
 
     // autoCallback provided
-    return Sequelize._clsRun(() =>
-      transaction.prepareEnvironment().then(() =>
-        autoCallback(transaction)
-      ).tap(() =>
-        transaction.commit()
-      ).catch(err =>
-        // Rollback transaction if not already finished (commit, rollback, etc) and reject with original error
-        Promise.try(() => {
-          // Rollback (ignore any error in rollback)
+    return Sequelize._clsRun(() => {
+      return transaction.prepareEnvironment()
+        .then(() => autoCallback(transaction))
+        .tap(() => transaction.commit())
+        .catch(err => {
+          // Rollback transaction if not already finished (commit, rollback, etc)
+          // and reject with original error (ignore any error in rollback)
+          return Promise.try(() => {
             if (!transaction.finished) return transaction.rollback().catch(function() {});
-        }).throw(err)
-      )
-    );
+          }).throw(err);
+        });
+    });
   }
 
   /**