automake: Add missing dependency for "check" target (fix parallel build)

Some unit tests use code from training. Those tests are enabled
if training is enabled, so for that case the "check" target
depends on the "training" target.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

Makefile.am

@@ -11,6 +11,8 @@ training-uninstall:
 	@$(MAKE) -C src/training uninstall
 clean-local:
 	@$(MAKE) -C src/training clean
+# Some unit tests use code from training.
+check: training
 else
 training:
 	@echo "Need to reconfigure project, so there are no errors"