build(package): simplify repository fields

created using @octoherd and https://github.com/gr2m/octoherd-script-normalize-package-repository-field

package.json

@@ -7,7 +7,7 @@
  "description": "Generated TypeScript definitions based on GitHub's OpenAPI spec",
  "main": "generated/types.js",
  "types": "generated/types.ts",
- "repository": "https://github.com/octokit/openapi-types.ts",
+ "repository": "github:octokit/openapi-types.ts",
  "keywords": [],
  "author": "Gregor Martynus (https://twitter.com/gr2m)",
  "license": "MIT",