fix(build): various small issues (#190)

- Persist all built files in CI.
- Ignore generated styles.
- Clean generated styles witn `npm run clean`.
- Update vis-dev-utils to fail the release if example screenshot
  generation fails.

.circleci/config.yml

@@ -54,7 +54,11 @@ jobs:
  - persist_to_workspace:
  root: ..
  paths:
+ - "repo/declarations"
  - "repo/dist"
+ - "repo/peer"
+ - "repo/standalone"
+ - "repo/styles"
 
  examples:
  executor: node

.gitignore

@@ -28,4 +28,5 @@ coverage/
 /examples/thumbnails/
 /peer/
 /standalone/
+/styles/
 vis-network-*.tgz