Fixed warning non-POSIX variable name

Ticket: CFE-2780
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

examples/Makefile.am

@@ -29,10 +29,10 @@ MAINTAINERCLEANFILES = Makefile.in mdate-sh
 
 # only re-run the outputs for examples that already have an example_output block
 remake:
-	perl ./remake_outputs.pl $(shell grep -l example_output $(dist_examples_DATA))
+	perl ./remake_outputs.pl `shell grep -l example_output $(dist_examples_DATA)`
 
 recheck:
-	perl ./remake_outputs.pl -c $(shell grep -l example_output $(dist_examples_DATA))
+	perl ./remake_outputs.pl -c `shell grep -l example_output $(dist_examples_DATA)`
 
 recheck_verbose:
-	perl ./remake_outputs.pl -v -c $(shell grep -l example_output $(dist_examples_DATA))
+	perl ./remake_outputs.pl -v -c `shell grep -l example_output $(dist_examples_DATA)`