Replaced literal brackets with LBRACKET and RBRACKET metacharacters

range2regex.go

@@ -115,7 +115,7 @@ func range2regex(start int, end int) string {
 			if startSlc[i] == endSlc[i] {
 				regex += string(rune(startSlc[i] + 48)) // '0' is ascii value 48, 1 is 49 etc. To convert the digit to its character form, we can just add 48.
 			} else {
-				regex += fmt.Sprintf("[%c-%c]", rune(startSlc[i]+48), rune(endSlc[i]+48))
+				regex += fmt.Sprintf("%c%c-%c%c", LBRACKET, rune(startSlc[i]+48), rune(endSlc[i]+48), RBRACKET)
 			}
 		}
 		regex += ")"