Use correct variable for path to server includes.

Alexander Korotkov · Alexander Korotkov · commit 7a30b5655188 · 2017-03-02T19:35:09.000+03:00
diff --git a/Makefile b/Makefile
@@ -38,4 +38,4 @@ maintainer-clean:
 install: installincludes
 
 installincludes:
-	$(INSTALL_DATA) $(addprefix $(srcdir)/, $(INCLUDES)) '$(DESTDIR)$(includedir)/server/'
+	$(INSTALL_DATA) $(addprefix $(srcdir)/, $(INCLUDES)) '$(DESTDIR)$(includedir_server)/'
