Feature/web3 eth iban es6 (web3#3964) (web3#3965)

* Feature/web3 eth iban es6 (web3#3964)

* web3-eth-iban es6 rewrite - replace `var` with `const` and `let`

* web3-eth-iban es6 rewrite - replace object prototype with class

* web3-eth-iban code style fix

Co-authored-by: Loredana <[email protected]>

* Update changelog

Co-authored-by: Loredana <[email protected]>

Author: spacesailor24

CHANGELOG.md

@@ -370,3 +370,4 @@ Released with 1.0.0-beta.37 code base.
 - Bump `elliptic` from `6.5.3` to `6.5.4` for `web3-eth-accounts` (#3941)
 - Bump `elliptic` from `6.5.3` to `6.5.4` for `web3-bzz` (#3940)
 - Bump `elliptic` from `6.5.3` to `6.5.4` for `web3-core-requestmanager` (#3945)
+- Rewrite `web3-eth-iban` in ES6 (#3955)