build-sys: use non-breaking spaces in contributor list

I think it's easier to read peoples' names with this change.

Makefile.am

@@ -6556,7 +6556,7 @@ print-%:
 	@echo $($*)
 
 git-contrib:
-	@git shortlog -s `git describe --abbrev=0`.. | cut -c8- | awk '{ print $$0 "," }' | sort -u
+	@git shortlog -s `git describe --abbrev=0`.. | cut -c8- | sed 's/ / /g' | awk '{ print $$0 "," }' | sort -u
 
 EXTRA_DIST += \
         tools/gdb-sd_dump_hashmaps.py