MSFT-15 Add lang attribute.

Author: gets0ul

__tests__/shared/__snapshots__/index.jsx.snap

@@ -5,6 +5,11 @@ exports[`Snapshot match 1`] = `
   <HelmetWrapper
     defer={true}
     encodeSpecialCharacters={true}
+    htmlAttributes={
+      Object {
+        "lang": "en",
+      }
+    }
   >
     <meta
       content="#FFFFFF"
@@ -34,6 +39,11 @@ exports[`Snapshot match 2`] = `
   <HelmetWrapper
     defer={true}
     encodeSpecialCharacters={true}
+    htmlAttributes={
+      Object {
+        "lang": "en",
+      }
+    }
   >
     <meta
       content="#FFFFFF"

src/shared/app.jsx

@@ -34,7 +34,7 @@ if (process.env.NODE_ENV === 'production') {
 export default function App() {
   return (
     <div>
-      <Helmet>
+      <Helmet htmlAttributes={{ lang: 'en' }}>
         <meta name="theme-color" content="#FFFFFF" />
         <link rel="manifest" href="/challenges/manifest.json" />
       </Helmet>