When I tried to utilize this package building my schema, I came across a bug that a type implementing multiple interfaces finally got only one interface in the transformed schema.
I found that your match RegEx and output code is different with what the spec defines:
currently this lib assumes multiple interfaces to be type D implements A, B, C, but according to spec, this ought to be type D implements A & B & C. Below is some reference.

• Is it possible to implement multiple interfaces in GraphQL? - Stack Overflow
• GraphQL Spec