remove a deprecation warning (#1459)

Author: devoncarew

lib/src/markdown_processor.dart

@@ -117,6 +117,7 @@ const validHtmlTags = const [
   "video",
   "wbr"
 ];
+
 final RegExp nonHTML =
     new RegExp("</?(?!(${validHtmlTags.join("|")})[> ])\\w+[> ]");
 
@@ -135,6 +136,8 @@ final RegExp isConstructor = new RegExp(r'^new[\s]+', multiLine: true);
 // Covers anything with leading digits/symbols, empty string, weird punctuation, spaces.
 final RegExp notARealDocReference = new RegExp(r'''(^[^\w]|^[\d]|[,"'/]|^$)''');
 
+final HtmlEscape htmlEscape = const HtmlEscape(HtmlEscapeMode.ELEMENT);
+
 final List<md.InlineSyntax> _markdown_syntaxes = [
   new _InlineCodeSyntax(),
   new _AutolinkWithoutScheme()
@@ -934,7 +937,7 @@ class _AutolinkWithoutScheme extends md.AutolinkSyntax {
   @override
   bool onMatch(md.InlineParser parser, Match match) {
     var url = match[1];
-    var text = md.escapeHtml(url).replaceFirst(_hide_schemes, '');
+    var text = htmlEscape.convert(url).replaceFirst(_hide_schemes, '');
     var anchor = new md.Element.text('a', text);
     anchor.attributes['href'] = url;
     parser.addNode(anchor);