Specify BSD-3-Clause license in package.json

The contents of `LICENSE` and `package.json` did not match.

Author: tali

package-lock.json

@@ -27,7 +27,7 @@
  "syntax"
  ],
  "author": "Sergey Romanov",
- "license": "MIT",
+ "license": "BSD-3-Clause",
  "bugs": {
  "url": "https://github.com/highlightjs/highlightjs-structured-text/issues"
  },