fix xref in pre-reqs

Author: hjwp

pre-requisite-installations.asciidoc

@@ -154,7 +154,7 @@ Here are a few tips:
     as in <<add-python-to-path>>,
     so that you can easily run Python from the command line.
 
-[[git-windows-defaut-editor]]
+[[git-windows-default-editor]]
 .Choose a nice default editor for Git
 image::images/git_windows_installer_choose_editor.png["Screenshot of Git installer"]