Added jupyterlab-spellcheck to environment.yml

Steps

[x] run git pull before you get started making branches or anything else. If you are the second one to walk through this exercise, you may get a merge conflict if you forget this step. That's because you are both editing the same file, so if you forget to pull the changes the other one made to the remote, github won't know what to do when you both ask it to change environment.yml in different ways
[x] Make sure you're in the correct directory
[x] Make a new dev branch, for Namita "dev-nam"
[x] Switch to branch with git checkout
[x] Activate Conda environment and launch jupyter lab
[x] Add to the environment file
[x] Check status
[x] git add, check status
[x] git commit with message
[x] Push the changes