Fixes #849

This feature adds support for ignoring .npmrc files in a repository. Set config option to true if you wish to ignore.

Closes #851

Previously, Renovate assumed that any yarn workspaces configuration would be in the root of the repository. Now, workspaces can be located within a subdirectory, e.g. `frontend/`. Note: Renovate still supports only one workspace per repository, please file an issue if you require more than one.

Closes #842 

Fixes #845

Now adds `stdout` and `stderr` from `npm` and `yarn` installs to the "Generated lockfile" log message, so that the exact versions of npm and yarn can be known in the default logs.

Closes #827

* fix: add upgrade and branch timings to log

Adds timing logs for upgrade detection + branch updating stages.

Closes #821

* improve request retry logging

`npm` and `yarn` lockfile generation use promisified child process `exec` now instead of `spawnSync`.

This fix improves the way Renovate detects embedded/installed npm and yarn. It tries:
- locally installed npm or yarn
- npm or yarn embedded inside globally installed renovate
- globally installed npm or yarn
- global `yarn` or `npm` commands as fallback

Fixes #824 

* chore(deps): update dependency prettier to v1.6.1

* chore(deps): update dependency prettier to v1.7.0

* run lint

* chore(deps): update dependency eslint-config-airbnb-base to v12.0.0

* fix lint