cjson: fix CMake imported targets

[SpaceIm]

Specify library name and version: cjson/all

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[conan-center-bot]

An unexpected error happened and has been reported. Help is on its way! 🏇

[conan-center-bot]

All green in build 2 (e2148a934a7557b8cab065fc6b352859da21959d)! 😊

• cjson/1.7.14: Generated 85 packages. All logs here
• cjson/1.7.13: Generated 85 packages. All logs here
• cjson/1.7.12: Generated 85 packages. All logs here