fix skeleton template makefile

IPython/nbconvert/templates/skeleton/Makefile

@@ -1,10 +1,10 b''
 
 
-all: tex/null.tplx tex/display_priority.tplx
+all: ../latex/skeleton/null.tplx ../latex/skeleton/display_priority.tplx
 
 # convert jinja syntax to tex
 # cf http://flask.pocoo.org/snippets/55/
-tex/%.tplx: %.tpl
+../latex/skeleton/%.tplx: %.tpl
 	@echo 'generating tex equivalent of $^: $@'
 	@echo '((= autogenerated file do not edit =))' > $@
 	@sed \
@@ -20,4 +20,4 b' tex/%.tplx: %.tpl'
 
 clean:
 	@echo "cleaning generated tplx files..."
-	@rm tex/*
+	@rm ../latex/skeleton/*