fix(): fixing unsafe usage of target="_blank" (#1604)

Author: vidarc

src/compiler/app-core/app-es5-disabled.ts

@@ -40,7 +40,7 @@ h2 {
   <h2>Developers:</h2>
   <ul>
     <li>ES5 builds are disabled <strong>during development</strong> to take advantage of 2x faster build times.</li>
-    <li>Please see the example below or our <a href="https://stenciljs.com/docs/stencil-config" target="_blank">config docs</a> if you would like to develop on a browser that does not fully support ES2017 and custom elements.</li>
+    <li>Please see the example below or our <a href="https://stenciljs.com/docs/stencil-config" target="_blank" rel="noopener noreferrer">config docs</a> if you would like to develop on a browser that does not fully support ES2017 and custom elements.</li>
     <li>Note that by default, ES5 builds and polyfills are enabled during production builds.</li>
     <li>When testing browsers it is recommended to always test in production mode, and ES5 builds should always be enabled during production builds.</li>
     <li><em>This is only an experiement and if it slows down app development then we will revert this and enable ES5 builds during dev.</em></li>
@@ -98,7 +98,7 @@ h2 {
   <h2 style="margin-top:0">AFTER:</h2>
   <p>The index.html should now include two scripts using the modern ES Module script pattern.
   Note that only one file will actually be requested and loaded based on the browser's native support for ES Modules.
-  For more info, please see <a href="https://developers.google.com/web/fundamentals/primers/modules#browser" target="_blank">Using JavaScript modules on the web</a>.
+  For more info, please see <a href="https://developers.google.com/web/fundamentals/primers/modules#browser" target="_blank" rel="noopener noreferrer">Using JavaScript modules on the web</a>.
   </p>
   <pre>
   <code>${escapeHtml(`<script`)} <span style="background:yellow">type="module"</span> src="/build/${config.fsNamespace}<span style="background:yellow">.esm</span>.js"${escapeHtml(`></script>`)}