Bump CMake version to avoid CMP0048 warning

[sloretz]

This bumps the minimum CMake version to 3.0.2, which is the minimum supported by ROS Kinetic and new enough to default to the NEW behavior of CMP0048. This avoids a CMake warning when building and testing this package in Debian Buster and Ubuntu Focal.

example:

==> Processing catkin package: 'robot_pose_ekf'
==> Building with env: '/home/sloretz/ws/noetic-misc/devel_isolated/tf/env.sh'
==> cmake /home/sloretz/ws/noetic-misc/src/robot_pose_ekf -DCATKIN_DEVEL_PREFIX=/home/sloretz/ws/noetic-misc/devel_isolated/robot_pose_ekf -DCMAKE_INSTALL_PREFIX=/home/sloretz/ws/noetic-misc/install_isolated -G Unix Makefiles in '/home/sloretz/ws/noetic-misc/build_isolated/robot_pose_ekf'
CMake Warning (dev) at CMakeLists.txt:2 (project):
  Policy CMP0048 is not set: project() command manages VERSION variables.
  Run "cmake --help-policy CMP0048" for policy details.  Use the cmake_policy
  command to set the policy and suppress this warning.

  The following variable(s) would be set to empty:

    CMAKE_PROJECT_VERSION
    CMAKE_PROJECT_VERSION_MAJOR
    CMAKE_PROJECT_VERSION_MINOR
    CMAKE_PROJECT_VERSION_PATCH
This warning is for project developers.  Use -Wno-dev to suppress it.

ros/catkin#1052