Use 3 space indent to support more than 3 levels of toc for GitLab

We found that 2 space indent can not show 3 levels of toc on GitLab, but 3
space indent fix this and doesn't break GitHub.

Signed-off-by: Chengwei Yang <[email protected]>

Author: chengweiv5

gh-md-toc

@@ -120,7 +120,7 @@ gh_toc_grab() {
     # format result line
     #   * $0 — whole string
     echo -e "$(awk -v "gh_url=$1" '{
-    print sprintf("%*s", substr($0, length($0), 1)*2, " ") "* [" substr($0, match($0, /a>.*<\/h/)+2, RLENGTH-5)"](" gh_url substr($0, match($0, "href=\"[^\"]+?\" ")+6, RLENGTH-8) ")"}' | sed 'y/+/ /; s/%/\\x/g')"
+    print sprintf("%*s", substr($0, length($0), 1)*3, " ") "* [" substr($0, match($0, /a>.*<\/h/)+2, RLENGTH-5)"](" gh_url substr($0, match($0, "href=\"[^\"]+?\" ")+6, RLENGTH-8) ")"}' | sed 'y/+/ /; s/%/\\x/g')"
 }
 
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