Nimbus CI: add nim-beacon-chain tests

We need to make sure that bumping Git submodules doesn't break
nim-beacon-chain here, since this is the recommeded setup for using that
repo.

.appveyor.yml

@@ -30,6 +30,7 @@ test_script:
   - build\nimbus.exe --help
   - mingw32-make -j2 ARCH_OVERRIDE=%PLATFORM% V=0 NIMFLAGS="-d:release" test
   - IF "%PLATFORM%" == "x64" mingw32-make -j2 test-reproducibility
+  - mingw32-make -C vendor/nim-beacon-chain -j2 V=0 test
 
 deploy: off
 

.travis.yml

@@ -37,4 +37,5 @@ script:
   - ./build/nimbus --help
   - make -j${NPROC} V=0 NIMFLAGS="-d:release" test
   - make -j${NPROC} V=0 test-reproducibility
+  - make -C vendor/nim-beacon-chain -j${NPROC} V=0 test