Handle peerDependencies

[bennypowers]

Consider the case of @apollo-elements/lit-apollo:

{
  "name": "@apollo-elements/lit-apollo",
  "version": "1.1.0",
  "module": "index.js",
  "dependencies": {
    "@apollo-elements/mixins": "^1.1.0"
  },
  "peerDependencies": {
    "lit-element": "^2.0.1",
    "lit-html": "^1.0.0"
  }
}

@apollo-elements/lit-apollo relies on @apollo-elements/lib which in turn relies on graphql-tag which has a peerDependency to graphql

pikawebification produces:

npx @pika/web                                                         24.8s
npx: installed 75 in 3.075s
⠼ @pika/web installing... @apollo-elements/lit-apollo
✖ 'lit-html' is imported by 'node_modules/@apollo-elements/lit-apollo/index.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'lit-element' is imported by 'node_modules/@apollo-elements/lit-apollo/index.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'lit-element' is imported by 'node_modules/@apollo-elements/lit-apollo/apollo-element.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'graphql/language/visitor' is imported by 'node_modules/apollo-client/bundle.esm.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'graphql/language/visitor' is imported by 'node_modules/apollo-utilities/lib/bundle.esm.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'graphql/language/parser' is imported by 'node_modules/graphql-tag/src/index.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'graphql/language/parser' is imported by 'commonjs-external-graphql/language/parser', but could not be resolved.
  Make sure that the file or package exists on disk.
✖ 'graphql/language/printer' is imported by 'node_modules/apollo-link/lib/bundle.esm.js', but could not be resolved.
  Make sure that the file or package exists on disk.
✔ @pika/web installed: @apollo-elements/lit-apollo. [1.50s]
⚠ Finished with warnings.

Perhaps pika/web should install those peerDeps?

[FredKSchott]

For now, @pika/web leaves the actual package installing to npm, and just focuses on web-ifying your deps. Re-reading that error message though, and I feel like it could be more friendly. What about:

"Make sure that the package was installed correctly and that the file exists."

[FredKSchott]

Fixed to a more friendly error message.