Add new favicon (#786)

public/index.html

       name="description"
       content="Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them."
     />
-    <meta name="image" content="https://excalidraw.com/og-image.png" />
+    <meta name="image" content="%PUBLIC_URL%/og-image.png" />
 
     <!-- OpenGraph tags -->
     <meta property="og:url" content="https://excalidraw.com" />
     <meta
       property="og:image"
       name="twitter:image"
-      content="https://excalidraw.com/og-image.png"
+      content="%PUBLIC_URL%/og-image.png"
     />
     <meta property="og:image:width" content="1280" />
     <meta property="og:image:height" content="669" />
       name="twitter:description"
       content="Excalidraw is a whiteboard tool that lets you easily sketch diagrams that have a hand-drawn feel to them."
     />
-    <meta name="twitter:image" content="https://excalidraw.com/og-image.png" />
+    <meta name="twitter:image" content="%PUBLIC_URL%/og-image.png" />
 
-    <link rel="icon" href="%PUBLIC_URL%/logo.png" />
+    <link
+      rel="shortcut icon"
+      href="%PUBLIC_URL%/favicon.ico"
+      type="image/x-icon"
+    />
     <link rel="stylesheet" href="%PUBLIC_URL%/fonts.css" />
     <link
       rel="preload"