layout adjustment

reader/src/main/res/layout/view_reading_mode_select.xml

@@ -7,6 +7,7 @@
     <TextView
         android:id="@+id/tv_readingMode"
         style="@style/Base.TextAppearance.AppCompat.Body1"
+        android:gravity="center_vertical"
         android:layout_width="0dp"
         android:layout_height="48dp"
         android:layout_marginEnd="16dp"