[ros-gazebo_plugins] fix shellcheck

Author: MatthijsBurgh

ros-gazebo_plugins/install.bash

@@ -9,14 +9,14 @@ then
 fi
 
 desired_version="2.9.2"
-installed_version=$(apt-cache policy ros-$TUE_ROS_DISTRO-gazebo-plugins | grep "Installed" | awk '{print $2}')
-if [ $installed_version == "(none)" ]
+installed_version=$(apt-cache policy ros-"$TUE_ROS_DISTRO"-gazebo-plugins | grep "Installed" | awk '{print $2}')
+if [ "$installed_version" == "(none)" ]
 then
     tue-install-debug "Not installed yet, so the newest version will be installed"
 elif version_gt "$desired_version" "$installed_version"
 then
     tue-install-echo "Going to install desired version($desired_version), current version: $installed_version"
-    tue-install-pipe sudo apt-get install --assume-yes -q ros-$TUE_ROS_DISTRO-gazebo-plugins
+    tue-install-pipe sudo apt-get install --assume-yes -q ros-"$TUE_ROS_DISTRO"-gazebo-plugins
 else
     tue-install-debug "Already on the desired version($desired_version): $installed_version"
 fi