message: Adds missing directory (axom/core) to Doxygen
diff: @@ -773,6 +773,7 @@ WARN_LOGFILE = dox.warnings
  INPUT = @PROJECT_SOURCE_DIR@/axom/mainpage.md \
  @PROJECT_SOURCE_DIR@/axom/core/README.md \
  + @PROJECT_SOURCE_DIR@/axom/core \
  @PROJECT_SOURCE_DIR@/axom/core/utilities \
  @PROJECT_SOURCE_DIR@/axom/core/numerics \
  @PROJECT_SOURCE_DIR@/axom/lumberjack \
  