Fix mcv dataset preparation
This pull request **introduces 1 alert** when merging c2593f8fe561b87c84cc95e892d8995a09a40592 into 29b1cbb91a96d97c4935739ea53bd3aa57214563 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-d327932951605936d384c4f20833f2afebe27fb5)

**new alerts:**

* 1 for Implicit string concatenation in a list This pull request **introduces 1 alert** when merging 389dda9092255c01f0aede60bad55deeb37cdba5 into 3436c5c01c3a1c52906fe51a6edc82a0a0d9bb50 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-eabc2cd68861cdcc6ba5c7c4b153c7035141e5ce)

**new alerts:**

* 1 for Implicit string concatenation in a list This pull request **introduces 1 alert** when merging 7b3225c7d5142906c072a7a1a6285997e4e46cea into aa0b2df346ad6976284cb9e5e74eb311004f24d3 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-c89c964b7a6f99f2d4b3881a49c1a01ac5b4a462)

**new alerts:**

* 1 for Implicit string concatenation in a list This pull request **introduces 1 alert** when merging c677d1ce0c70de3b145c92f618d02a2625031165 into da48c997177f89a9e305e508ab27b15954044814 - [view on LGTM.com](https://lgtm.com/projects/g/NVIDIA/NeMo/rev/pr-3e83d49170526fc7a92ffb270d22cf87931e9a9c)

**new alerts:**

* 1 for Implicit string concatenation in a list
# Changelog
- Update MCV dataset preparation script to utilize v6.1 dataset 