fix: pass through numeric character references as is representing < and &, as otherwise may break well-formedness; fixes svg#1

Author: brettz9

lib/sax.js

@@ -827,6 +827,11 @@
         num = parseInt(entity, 10)
         numStr = num.toString(10)
       }
+      switch (num) {
+        case 60: // '<'
+        case 38: // '&'
+          return '&' + entityLC + ';'
+      }
     }
     entity = entity.replace(/^0+/, '')
     if (isNaN(num) || numStr.toLowerCase() !== entity) {