Example grammars: Improve |parseInt| invocations

Instead of |parseInt("0x" + digits)| do |parseInt(digits, 16)|, which is
a bit cleaner.

examples/css.pegjs

@@ -298,7 +298,7 @@ nonascii
 
 unicode
   = "\\" digits:$(h h? h? h? h? h?) ("\r\n" / [ \t\r\n\f])? {
-      return String.fromCharCode(parseInt("0x" + digits));
+      return String.fromCharCode(parseInt(digits, 16));
     }
 
 escape

examples/javascript.pegjs

@@ -231,7 +231,7 @@ SignedInteger
   = [-+]? DecimalDigits
 
 HexIntegerLiteral
-  = "0" [xX] digits:$HexDigit+ { return parseInt("0x" + digits); }
+  = "0" [xX] digits:$HexDigit+ { return parseInt(digits, 16); }
 
 HexDigit
   = [0-9a-fA-F]
@@ -292,12 +292,12 @@ EscapeCharacter
 
 HexEscapeSequence
   = "x" digits:$(HexDigit HexDigit) {
-      return String.fromCharCode(parseInt("0x" + digits));
+      return String.fromCharCode(parseInt(digits, 16));
     }
 
 UnicodeEscapeSequence
   = "u" digits:$(HexDigit HexDigit HexDigit HexDigit) {
-      return String.fromCharCode(parseInt("0x" + digits));
+      return String.fromCharCode(parseInt(digits, 16));
     }
 
 RegularExpressionLiteral "regular expression"

examples/json.pegjs

@@ -65,7 +65,7 @@ char
   / "\\r"  { return "\r"; }
   / "\\t"  { return "\t"; }
   / "\\u" digits:$(hexDigit hexDigit hexDigit hexDigit) {
-      return String.fromCharCode(parseInt("0x" + digits));
+      return String.fromCharCode(parseInt(digits, 16));
     }
 
 number "number"