Tiny typo fix

.circleci/config.yml

@@ -37,7 +37,7 @@ jobs:
           # nixpkgs we selected will be used everywhere Nix pulls in software.
           # There is no way to set an environment variable containing the
           # value of another environment variable on CircleCI except to use
-          # the `BASE_ENV` feature as we do here.
+          # the `BASH_ENV` feature as we do here.
           name: "Setup NIX_PATH Environment Variable"
           command: |
             echo "export NIX_PATH=nixpkgs=https://github.com/NixOS/nixpkgs/archive/$NIXPKGS_REV.tar.gz" >> $BASH_ENV