Use cleaner integer bump syntax

bin/dissect_url

@@ -19,7 +19,7 @@ main() {
         while read -r url;
         do
             if [[ -z "$url" ]]; then exit 0; fi
-            i=`expr $i + 1`
+            ((i++))
             printf '=== url %02d =============================================\n' $i
             dissect "$url"
         done