Fixed broken link in documentation.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "CanvasGradient": {
       "comment": [
         "/**",
         " * An opaque canvas object representing a gradient.",
         " *",
         " * Created by calling [createLinearGradient] or [createRadialGradient] on a",
         " * [CanvasRenderingContext2D] object.",
         " *",
@@ skipping 518 matching lines @@
           "   * The response is processed as",
           "   * `text/xml` stream, unless responseType = 'document' and the request is",
           "   * synchronous.",
           "   */"
         ],
         "send": [
           "/**",
           "   * Send the request with any given `data`.",
           "   *",
           "   * See also:",
-          "   * [send() docs](https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#send())",
+          "   *",
+          "   *   * [send](https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#send%28%29)",
           "   * from MDN.",
           "   */"
         ],
         "status": [
           "/**",
           "   * The http result code from the request (200, 404, etc).",
           "   * See also: [Http Status Codes](http://en.wikipedia.org/wiki/List_of_HTTP_status_codes)",
           "   */"
         ],
         "statusText": [
@@ skipping 49 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }