use let/const es6 syntax for, forin, forof

[mrbbp]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

sorry first time,

i use the for, forin and for...of snippets but my linter configured to works with es6 is unhappy. so i propose the change var to more contemporary variable declaration let and const

Alternate Designs

Benefits

more contemporary variable declaration

Possible Drawbacks

possibly confused for beginners

Applicable Issues

perhaps a prob with old navigator

[apicgg]

This makes sense. Thanks. @sadick254 Could you please merge this to master? It will be really helpful to have 'let' instead of 'var'.