nodejs: export DESTDIR to fix build with dash

* when building on machine with /bin/sh -> /bin/dash
  DESTDIR is empty in install and it's trying to write to /usr/include and fails

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
nodejs-0.8.18: export DESTDIR to fix build with dash

* when building on machine with /bin/sh -> /bin/dash
  DESTDIR is empty in install and it's trying to write to /usr/include and fails

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>