Remove unused pegjs devDependency #12

Why

The top-level pegjs devDependency in package.json is not used by anything in this repository.

• The build (gulp build) compiles src/tag-data.peg through gulp-peg@0.1.2, which declares its own dependency pegjs ^0.8.0. After npm install, npm ls pegjs shows that gulp-peg resolves its own nested pegjs@0.8.0; the top-level pegjs is never loaded by the build.
• No source, test, or config file requires pegjs, and no npm script calls the pegjs CLI. The tests load the committed dist/parser.js (generated by PEG.js 0.8.0).
• pegjs was added together with gulp-peg in 43407df and has never been imported since.

Keeping it means Dependabot keeps opening bump PRs (e.g. #8, pegjs 0.8.0 → 0.10.0) that have no effect on the build or the published dist/ files.

What

Implementation target: increments/tag-data-parser.

Remove the pegjs entry from devDependencies in package.json.

Non-goals:

• Upgrading the PEG.js version used to generate dist/parser.js (that is controlled by gulp-peg's own dependency).
• Replacing gulp / gulp-peg.

TODO

• Remove pegjs from devDependencies in package.json
• Confirm npm install and npm test still pass
• Close Bump pegjs from 0.8.0 to 0.10.0 #8 after the removal is merged

Ref

• Bump pegjs from 0.8.0 to 0.10.0 #8