Fix 0XDEADBEEF not recognised by some Perls

They do recognise 0xDEADBEEF, but not 0XDEADBEEF.
So, use lc.

Example of one of many test failures:

  Failed test 'result: number: heX'
     at t/001_simple_types.t line 18.
          got: '0'
     expected: '3735928559'
  Looks like you failed 1 test of 67.
force minimum perl to 5.10.0