Makefile check for submodules

[roncewind]

In order to build the dockerfile, sub-modules are required.

to do this one must update or pull in the submodules:

rm -rf senzing-rest-api-specification
git submodule update --init

or if cloning new use:
https://github.com/Senzing/knowledge-base/blob/master/HOWTO/clone-repository.md

we should be able to do this as part of the makefile.