[RT#89098] Module::Build::Tiny and destdir

As mentioned in the Module::Build::Tiny docs, the destdir parameter should be --destdir:

 Module::Build has an extremely permissive way of argument
 handling, Module::Build::Tiny only supports a (sane) subset of
 that. In particular, ./Build destdir=/foo does not work, you will
 need to pass it as ./Build --destdir=/foo.

Untested patch attached which should resolve this.

Signed-off-by: Chris 'BinGOs' Williams <chris@bingosnet.co.uk>