fix(analytics): Use gtag

src/App.tsx

@@ -37,16 +37,20 @@ const App: React.SFC<ISiteData> = ({ author, siteName, googleAnalytics }) => {
           href="https://fonts.googleapis.com/css?family=Roboto:300,400,500,700"
           type="text/css"
         />
+        {addAnalytics && (
+          <script
+            async
+            src={`https://www.googletagmanager.com/gtag/js?id=${googleAnalytics}`}
+          />
+        )}
         {addAnalytics && (
           <script>
             {`
-              (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
-              (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
-              m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
-              })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');
-              ga('create', '${googleAnalytics}', 'auto');
-              ga('send', 'pageview');
-            `.replace(/\s+/g, ' ')}
+              window.dataLayer = window.dataLayer || [];
+              function gtag(){dataLayer.push(arguments);}
+              gtag('js', new Date());
+              gtag('config', '${googleAnalytics}');
+            `}
           </script>
         )}
       </Head>
@@ -55,10 +59,12 @@ const App: React.SFC<ISiteData> = ({ author, siteName, googleAnalytics }) => {
           <Route
             path="/"
             render={({ location }) => {
-              const ga = typeof window !== 'undefined' && (window as any).ga;
-              if (ga) {
-                ga('set', 'page', location.pathname + location.search);
-                ga('send', 'pageview');
+              const gtag =
+                typeof window !== 'undefined' && (window as any).gtag;
+              if (addAnalytics && gtag) {
+                gtag('config', googleAnalytics, {
+                  page_path: location.pathname + location.search,
+                });
               }
               return null;
             }}