Update article.md

string with backslash is "1\\2"
"1\2" is 1 and \2  
Error: Octal escape sequences are not allowed in strict mode.
without strict mode match returns null

5-regular-expressions/04-regexp-escaping/article.md

@@ -30,7 +30,7 @@ alert( "function g()".match(/g\(\)/) ); // "g()"
 If we're looking for a backslash `\`, then we should double it:
 
 ```js run
-alert( "1\2".match(/\\/) ); // '\'
+alert( "1\\2".match(/\\/) ); // '\'
 ```
 
 ## A slash