fixes #150, broken code in js_number.dart

lib/runtime/dart/_interceptors.js

Index: lib/runtime/dart/_interceptors.js
diff --git a/lib/runtime/dart/_interceptors.js b/lib/runtime/dart/_interceptors.js
index f9b0df9757b8ab8be84ee83059079dcc5a01bb06..ca2bb15fb2d950520c37a55401db8912a4b67c22 100644
--- a/lib/runtime/dart/_interceptors.js
+++ b/lib/runtime/dart/_interceptors.js
@@ -205,7 +205,7 @@ var _interceptors;
       if (match == null) {
         throw new core.UnsupportedError(`Unexpected toString result: ${result}`);
       }
-      let result = dart.dindex(match, 1);
+      result = dart.dindex(match, 1);
       let exponent = +dart.dindex(match, 3);
       if (dart.dindex(match, 2) != null) {
         result = result + dart.dindex(match, 2);