@apollo/federation minification bug

There seems to be an issue when using buildFederatedSchema while minified. Per the documentation, when you're using federation, you are expected to use the extend keyword on types that will be merged with other schemas:

extend type Query {
  ping: String!
}

This syntax breaks when minified, causing the error:

Error: Cannot extend type "Query" because it is not defined.

Steps to replicate:

• Clone this repository
• run yarn or npm install to install the depedencies
• run yarn start or npm start to run the non-minified code. You will see the output line "Built"
• run yarn bug or npm run bug to minify and run the minified code. The expected result would be to see "Built" again. The actual result is that it errors out with the aforementioned error.