algo/test/Makefile: Issue when file doesn't have line return at its end

As some files didn't have line returns at their end, this could come some issue.
We instead use awk, which solves the problem.
(Thanks to muru: https://unix.stackexchange.com/a/420622)

See #2259

algo/tests/Makefile

@@ -98,7 +98,7 @@ shouldvdj_with_rc:
 	$(SHOULD_VDJ_TO_TAP) -r $(SHOULD_VDJ)
 
 shouldvdj_with_rc_merged:
-	cat $(SHOULD_VDJ) > should-vdj-tests/should-vdj.merged.fa
+	awk 1  $(SHOULD_VDJ) > should-vdj-tests/should-vdj.merged.fa
 	$(SHOULD_VDJ_TO_TAP) -r should-vdj-tests/should-vdj.merged.fa
 
 # When the global test suite is passing, individual failed tests (tagged with BUG or BUG-LOCUS in the *.should-vdj.fa files)