Update CMakeLists.txt (#247)

(cherry picked from commit 52abdf5)

Author: rafal-gorecki

micro_ros_agent/CMakeLists.txt

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.11)
 
 option(UROSAGENT_GENERATE_PROFILE
   "Generates agent.refs according to the .msgs provided in the .repos" OFF