Restricting exit nodes in torrc fails silently

When using @ExitNodes@ to restrict exits to one country, an error in syntax causes this option to fail silently when using Tor Browser.

For example, this code works:

ExitNodes {GB}
StrictNodes 1

While this code fails:

ExitNodes {uk}
StrictNodes 1

Spotted on v7.0.1 (64-bit) on Mac OSX 10.11.5 (15F34)