Backslash-u encode non-ascii characters

Issue #3474

Author: marijnh

lib/codemirror.js

@@ -6952,7 +6952,7 @@
           txt.setAttribute("cm-text", "\t");
           builder.col += tabWidth;
         } else if (m[0] == "\r" || m[0] == "\n") {
-          var txt = content.appendChild(elt("span", m[0] == "\r" ? "␍" : "␤", "cm-invalidchar"));
+          var txt = content.appendChild(elt("span", m[0] == "\r" ? "\u240d" : "\u2424", "cm-invalidchar"));
           txt.setAttribute("cm-text", m[0]);
           builder.col += 1;
         } else {