Add missing dependency (#20)

Author: garyservin

json_transport/package.xml

@@ -41,6 +41,7 @@ OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   <depend>json_msgs</depend>
   <depend>nlohmann-json-dev</depend>
   <depend>roscpp</depend>
+  <depend>python3-jsonschema</depend>
 
   <test_depend>catkin_virtualenv</test_depend>
   <test_depend>roslint</test_depend>