- client: Don't unregister field 'Upstream DNS servers' on rerender and allow input text continuously

Close #1752

Squashed commit of the following:

commit 2f86ade71eadd648fe3e62d8f619d5f1419d6527
Author: ArtemBaskal <a.baskal@adguard.com>
Date:   Fri May 29 10:58:42 2020 +0300

    - client: Don't unregister field 'Upstream DNS servers' on rerender and allow input text continuously

client/src/components/Settings/Dns/Upstream/Form.js

@@ -5,7 +5,6 @@ import { Field, reduxForm, formValueSelector } from 'redux-form';
 import { Trans, withTranslation } from 'react-i18next';
 import flow from 'lodash/flow';
 import classnames from 'classnames';
-import { nanoid } from 'nanoid';
 
 import Examples from './Examples';
 import { renderRadioField } from '../../../../helpers/form';
@@ -63,7 +62,7 @@ let Form = (props) => {
         <div className="row">
             {INPUT_FIELDS.map(({
                 name, component, type, className, placeholder, getTitle, subtitle, disabled, value,
-            }) => <div className="col-12 mb-4" key={nanoid()}>
+            }) => <div className="col-12 mb-4" key={placeholder}>
                 {typeof getTitle === 'function' && getTitle()}
                 <Field
                     id={name}