BUG: Be compliant with new cmake policy CMP0072 with cmake > 3.11

fix bug #1653 (closed) fix a typo in a comment in a cmakelists.txt

The issue pop up of pc-christophe with a recent version of cmake:

https://dash.orfeo-toolbox.org/viewConfigure.php?buildid=325190

Our cmake policy management in OTB cmake deserves some love as we maintain for historical reason OLD behaviour for cmake policies (46 and 54).

It should be ported to the NEW behavior and not rely on setting a policy to OLD.