Rename components "Shared" folder to "shared"

app/javascript/components/shared/Spinner.tsx

@@ -0,0 +1,9 @@
+import * as React from 'react';
+
+const Spinner = () => (
+  <div className="spinner-border d-block mx-auto" role="status">
+    <span className="sr-only">Loading...</span>
+  </div>
+);
+
+export default Spinner;