add mass in rom urdf

data/urdf/anymal_trunk.urdf

 <robot name="anymal_all">
   <link name="base_link">
+  <inertial>
+     <mass value="30.47"/>
+     <inertia ixx="1." ixy="0.0" ixz="0.0" iyy="1." iyz="0.0" izz="1."/>
+  </inertial>
     <visual>
       <origin xyz="0 0 0" rpy="0 0 0" />
       <geometry>