Update telling-git-about-your-signing-key.md

Edited the ZSH shell command to use the proper denotation for the TTY variable.

Author: jackverstraate

content/authentication/managing-commit-signature-verification/telling-git-about-your-signing-key.md

@@ -36,8 +36,8 @@ If you have multiple GPG keys, you need to tell Git which one to use.
 1. If you aren't using the GPG suite, run the following command in the `zsh` shell to add the GPG key to your `.zshrc` file, if it exists, or your `.zprofile` file:
 
    ```shell
-   $ if [ -r ~/.zshrc ]; then echo -e '\nexport GPG_TTY=$(tty)' >> ~/.zshrc; \
-     else echo -e '\nexport GPG_TTY=$(tty)' >> ~/.zprofile; fi
+   $ if [ -r ~/.zshrc ]; then echo -e '\nexport GPG_TTY=$TTY' >> ~/.zshrc; \
+     else echo -e '\nexport GPG_TTY=$TTY' >> ~/.zprofile; fi
    ```
 
    Alternatively, if you use the `bash` shell, run this command: