NPM dependencies as externals causes a warning

[AntonPilyak]

• Rollup Version: 1.1.2
• Operating System (or Browser): Win10
• Node Version: 10.15.0

How Do We Reproduce?

In Typescript project (didn't check if it is the same with plain JS)

1. install npm dependencies using this or similar config. Here is the more detailed example.
2. mark installed packages as externals, like it is described here
3. build the bundle.

Expected Behavior

No warnings, NPM dependencies are not exported from the bundle.

Actual Behavior

"(!) Missing global variable names" warning for installed NPM dependencies

[AntonPilyak]

The issue was my mistake related to umd modules imports.