Add supports-color as optional peerDependency

[jgierer12]

This is the proper way to declare this type of dependency.

Note that if peerDependenciesMeta is not supported by the package
manager (yarn < 1.13 and npm) and supports-color is not installed, a warning will be
displayed.

See peerDependencies, peerDependenciesMeta.

Without this, Yarn PnP to throws an error when debug is in the dependency tree, since PnP is very strict about requireing packages that aren't declared as dependencies.

[coveralls]

Coverage remained the same at 87.692% when pulling 46b89a5 on jgierer12:supports-color-optional-peer-dep into 5c7c61d on visionmedia:master.

[eps1lon]

Quick update that peerDependenciesMeta is implemented in yarn@1.13.0, npm@6.11.0 but not yet bundled with node and pnpm@?

I'm currently not using this feature myself until node bundles npm@6.11. If there are any concerns about this feature please let me know.

original RFC

[arcanis]

Note that the situation changed since the last comment. The peerDependenciesMeta is supported by all modern package managers (at least 6 month old).

Additionally, listing peerDependenciesMeta is enough for the peer dependency to be inferred even without the peerDependencies field being set - providing a smooth adoption path even for older package managers.

CC @Qix-

[Qix-]

Published as 4.2.0 under the beta dist-tag. Please test and make sure nothing has broken for you before I send to latest.