Compile fix

Author: adalpari

WordPress/src/main/java/org/wordpress/android/ui/reader/views/ReaderSiteHeaderView.java

@@ -13,6 +13,8 @@
 import android.widget.ProgressBar;
 import android.widget.TextView;
 
+import androidx.annotation.Nullable;
+
 import org.wordpress.android.R;
 import org.wordpress.android.WordPress;
 import org.wordpress.android.datasets.ReaderBlogTable;