finish part 2

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-book/src/lsm-tutorial/week2-00-leveled.svg

@@ -8,7 +8,7 @@
       </g>
     </marker>
   </defs>
-  <g id="week2-00-leveled" stroke-opacity="1" fill-opacity="1" stroke-dasharray="none" stroke="none" fill="none">
+  <g id="week2-00-leveled" fill="none" stroke="none" fill-opacity="1" stroke-dasharray="none" stroke-opacity="1">
     <title>week2-00-leveled</title>
     <rect fill="white" x="85" y="204" width="473" height="245"/>
     <g id="week2-00-leveled_Layer_1">