Fix location of symlinks to generate manpages

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

debian/rules

@@ -32,7 +32,7 @@ override_dh_missing:
 	dh_missing --fail-missing
 
 execute_before_dh_installman:
-	cd $(CURDIR)/debian/rust-coreutils/usr/lib/cargo/bin/coreutils/; \
+	cd $(CURDIR)/debian/rust-coreutils/usr/bin/; \
 	for f in *; do \
 		filename=$$(basename $$f); \
 		help2man --no-info $$f > $(CURDIR)/docs/$$filename.1; \