Fix erroneous snippet index in git lesson

Signed-off-by: Matt Oswalt <[email protected]>

Author: Mierdin

lessons/fundamentals/lesson-17-git/stage1/guide.md

@@ -61,7 +61,7 @@ Once we've used `git add` to include all the changes we want to commit into stag
 ```
 git commit -m "My first commit!"
 ```
-<button type="button" class="btn btn-primary btn-sm" onclick="runSnippetInTab('linux1',5)">Run this snippet</button>
+<button type="button" class="btn btn-primary btn-sm" onclick="runSnippetInTab('linux1', this)">Run this snippet</button>
 
 > Note the use of the `-m` flag to specify the commit message inline - you can omit this if you wish, and Git will open a text editor for you to specify your commit message