doc: Fix some typos in scons_script_how_to.txt

doc: Fix some typos in scons_script_how_to.txt

Maybe this file worth to be migrated to iotivity wiki in a scons page

Change-Id: I288da1273621a48add047993506ed40c107363ab
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/11077
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Ziran Sun <ziran.sun@samsung.com>
(cherry picked from commit da851aa0583bb1fcccfa634de8b61ee815fbdbd8)
Reviewed-on: https://gerrit.iotivity.org/gerrit/12109