no issue
- Updated Test & linting packages
- Updated use of hasOwnProperty
- Using Object.prototype.hasOwnProperty instead (ref. eslint.org/docs/rules/no-prototype-builtins)
- Removed already defined built-in global variable Intl
- Applied `--fix` with lint command on `core/test` folder
- The rules were broken because some of them were made stricter for `eslint: recommended` ruleset (ref. https://eslint.org/docs/user-guide/migrating-to-6.0.0#eslint-recommended-changes)
- Removed redundant global variable declarations to pass linting
