Added an old co-polymer id

Author: egonw

data/cas.tsv

@@ -24,6 +24,7 @@
 126639-29-0		117-81-7
 131891-38-8		79-94-7
 137718-37-7		117-81-7
+138454-81-6		29658-26-2
 152175-96-7		12184-96-2
 152175-97-8		12596-12-2
 153012-39-6		55268-75-2