Update flag for nbval

Author: takluyver

Makefile

@@ -38,7 +38,7 @@ test-quick:
 
 
 test-ipynb: create-dirs
-	cd doc/ipynb && py.test . -v --ipynb --sanitize-with sanitize_file --junitxml=$(PROJECT_DIR)/test-reports/junit/test-ipynb-pytest.xml
+	cd doc/ipynb && py.test . -v --nbval --sanitize-with sanitize_file --junitxml=$(PROJECT_DIR)/test-reports/junit/test-ipynb-pytest.xml
 
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