Assert SyntaxError with lower bound in escape seq.

ES2015 reads:

> RegExpUnicodeEscapeSequence :: u{ HexDigits }
>
> - It is a Syntax Error if the MV of HexDigits > 1114111.

Use the MV 0x110000 to assert the lower boundary of values which are
expected to produce the SyntaxError.

test/language/literals/regexp/u-unicode-esc-bounds.js

@@ -13,4 +13,4 @@ info: >
 negative: SyntaxError
 ---*/
 
-/\u{ff0000}/u;
+/\u{110000}/u;