fix typo

book/mobile.html

@@ -124,7 +124,7 @@ <h1><a href="index.html" style="text-decoration:none;">Robotic Manipulation</a><
     <p>For table-top manipulation, we started by assuming known objects and
     then discussed approaches (such as antipodal grasping) that could work on
     unknown objects. But throughout that discussion, we always assumed that we
-    new the geometry and location of the table / bins! For instance, we
+    knew the geometry and location of the table / bins! For instance, we
     actively cropped away the point cloud returns that hit the known
     environment and left only points associated with the objects. That's a very
     reasonable thing to do when your robot is bolted to the table, but we need