clean-up trailing whitespace (#453)

These changes have been mostly auto-generated with:

	find . -type f -print0 | xargs -0 perl -pi -e 's/ +$//'

Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

exercises/source_routing/s3-runtime.json

@@ -3,4 +3,4 @@
   "p4info": "build/source_routing.p4.p4info.txt",
   "bmv2_json": "build/source_routing.json",
   "table_entries": [ ]
-} 
+}