scripts: relnotes: fix path to limitations.md
scripts: relnotes: fix path to limitations.md

When we moved the script to a new directory we broke the relpath
link to the limitations.md file. Fix it.

Fixes: #519

Signed-off-by: Graham Whaley <95f36e5ac6982f4574a5c449c37cf652e934d2b9@intel.com>

clearcontainers/runtime,clearcontainers/runtime,devimc/runtime,chavafg/runtime,devimc/runtime,chavafg/runtime