fix compile error if missing extern create rand;

[xiiiAtCn]

What to expect when you open a pull request here

2018 Edition

The 2018 is a "living" edition; it's not scheduled for in-print publication at
this time, and so is able to be updated at any time. We'd love pull requests to
fix issues with this edition, but we're not interested in extremely large
changes without discussing them first. If you'd like to make a big change,
please open an issue first! We'd hate for you to do some hard work that we
ultimately wouldn't accept.

Second edition

No Starch Press has brought the second edition to print. Pull requests fixing
factual errors will be accepted and documented as errata; pull requests changing
wording or other small corrections should be made against the 2018 edition instead.

First edition

The first edition is frozen, and no longer accepting changes. Pull requests
made against it will be closed.

Thank you for reading, you may now delete this text!

[dralley]

extern create is misspelled. However, it shouldn't be necessary in 2018 edition Rust. If you're using the most recent version of Rust and you create a new project, this should compile fine I believe.

[carols10cents]

Yes, this is intentional. You may have been confused by the lack of edition="2018" in the Cargo.toml at the beginning of the chapter; that is being fixed in #1671.