[ProjectSample] Add unknownDefines to off

This is to avoid this compile error:
info ProjectSample Parsing dependencies
info ProjectSample Compiling 338 sources
ERR! compile ERROR - unknown @define variable goog.json.USE_NATIVE_JSON
ERR! compile
ERR! compile
ERR! compile 1 error(s), 0 warning(s),
ERR! compile 97.6
ERR! compile % typed