Downgrade es6-promise version to match version used with bower

In the es6-promise v4 the default behavior was changed compared to the
v3. In v3 polyfill installs automatically, while in v4 the es6-promise.js
file doesn't install polyfill by default. With the v4 application can
either use a different file (es6-promise.auto.js) or call
Promise.polyfill() method.

The version 3 was used before with bower components. There is no reason
to upgrade this library, so it is safer to use the same version.

Change-Id: Ifebb10da864d012b33fb25e6301245b434b8fff5

polygerrit-ui/app/package.json

@@ -25,7 +25,7 @@
     "@polymer/polymer": "^3.3.0",
     "@webcomponents/shadycss": "^1.9.2",
     "@webcomponents/webcomponentsjs": "^1.3.3",
-    "es6-promise": "^4.2.8",
+    "es6-promise": "^3.3.1",
     "moment": "^2.24.0",
     "page": "^1.11.5",
     "polymer-bridges": "file:../../polymer-bridges/",

polygerrit-ui/app/yarn.lock

@@ -328,10 +328,10 @@
 "ba-linkify@file:../../lib/ba-linkify/src":
   version "1.0.0"
 
-es6-promise@^4.2.8:
-  version "4.2.8"
-  resolved "https://registry.yarnpkg.com/es6-promise/-/es6-promise-4.2.8.tgz#4eb21594c972bc40553d276e510539143db53e0a"
-  integrity sha512-HJDGx5daxeIvxdBxvG2cb9g4tEvwIk3i8+nhX0yGrYmZUzbkdg8QbDevheDB8gd0//uPj4c1EQua8Q+MViT0/w==
+es6-promise@^3.3.1:
+  version "3.3.1"
+  resolved "https://registry.yarnpkg.com/es6-promise/-/es6-promise-3.3.1.tgz#a08cdde84ccdbf34d027a1451bc91d4bcd28a613"
+  integrity sha1-oIzd6EzNvzTQJ6FFG8kdS80ophM=
 
 isarray@0.0.1:
   version "0.0.1"