fix(package.json) fix failing test suite
fix(package.json) fix failing test suite

- Fix missing `mocha` package devDependency that was causing test suite to fail to work.

Reason for the change:
- Test suite fails without of the required dependencies.

Related issue:
- #1117 https://github.com/SC5/sc5-styleguide/issues/1117
  - "Test suite fails to run without mocha dependency"

junaidrsd/sc5-styleguide,SC5/sc5-styleguide,patriziosotgiu/sc5-styleguide,junaidrsd/sc5-styleguide,SC5/sc5-styleguide,varya/sc5-styleguide,varya/sc5-styleguide,patriziosotgiu/sc5-styleguide