Update keyword highlighting

Author: sparkprime

doc/_layouts/default.html

@@ -40,7 +40,7 @@
       'boolean': /\b(true|false)\b/g,
       'constant': /\bnull\b/g,
       'error': /\berror\b/g,
-      'special': /\b(local|function|if|then|else|import|importstr|for|in)\b/g,
+      'special': /\b(assert|tailstrict|local|function|if|then|else|import|importstr|for|in)\b/g,
       'number': /\b[0-9][0-9.eE]*\b/g,
       'operator': /(\+|\*|\/)+/g,
     };