tools: Add patch command to "git diff"

- May as well let the changes be easily removed.

eris/tools.toml

@@ -128,6 +128,7 @@ tools_for_extensions = [
   dependencies = ["git"]
   url = "https://git-scm.com/docs/git-diff"
   command = "git diff --exit-code"
+  patch_command = "git checkout"
   has_color = true
 
 [git_blame]