Update install_ubuntu.md

Signed-off-by: Yaswanth <92177410+yaswanth1701@users.noreply.github.com>

Author: yaswanth1701

harmonic/install_ubuntu.md

@@ -10,6 +10,7 @@ WARNING: for gazebo-classic (eg. `gazebo11`) users: `gz-harmonic` cannot be
 installed alongside with `gazebo11` by default. To facilitate the migration
 this can be done using the instruction detailed in
 [Installing Gazebo11 side by side with new Gazebo](/docs/all/install_gz11_side_by_side).
+
 </div>
 
 First install some necessary tools: