fixed _header.html being replaced by _footer.html

rivet.sh

@@ -139,9 +139,9 @@ mv "$tmpsed" "$headerfile"
 sed 's/<\/header>//' "$headerfile" > "$tmpsed"
 mv "$tmpsed" "$headerfile"
 sed 's/<footer.*>//' "$footerfile" > "$tmpsed"
-mv "$tmpsed" "$headerfile"
+mv "$tmpsed" "$footerfile"
 sed 's/<\/footer>//' "$footerfile" > "$tmpsed"
-mv "$tmpsed" "$headerfile"
+mv "$tmpsed" "$footerfile"
 
 # Remove any junk from the domain eg. [https://]domain.com[/]
 domain="$(echo "$2" | sed -e 's/^https*:\/\///' -e 's/\/$//')"