Update to doctoc v2 & simplify call pattern

[eemeli]

This also adds a check to the lint task to validate the current TOCs.

[ochameau]

Looks good, thanks for all the help on maintaining all this!

Note that I see local differences when running npm run toc:

$ git diff
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9b1339a..8372704 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -14,6 +14,7 @@ and introduce yourself.
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
- [Filing Issues](#filing-issues)
- [Building From Source](#building-from-source)
- [Submitting Pull Requests](#submitting-pull-requests)
diff --git a/README.md b/README.md
index 1d2741d..21e2261 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,7 @@ This is a library to generate and consume the source map format
<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
- [Examples](#examples)
- [Consuming a source map](#consuming-a-source-map)
- [Generating a source map](#generating-a-source-map)

[eemeli]

@ochameau:
Note that I see local differences when running npm run toc: [...]

Did you run npm install to update doctoc, or is that with its latest version?