Normalize use of string in git command.

"gpgSign" instead of "gpgsign" for both invocations: (a) avoids confusion, (b) matches use of camel case as in Git documentation.

Author: kakkeshyor

data/reusables/gpg/set-auto-sign.md

@@ -1,7 +1,7 @@
 1. Optionally, to configure Git to sign all commits and tags by default, enter the following command:
 
    ```shell
-   git config --global commit.gpgsign true
+   git config --global commit.gpgSign true
    git config --global tag.gpgSign true
    ```