Supports Optional Chaining

[ota-meshi]

And change the supported version of ESLint from 6.0.0 to 6.2.0.

Core

• Change presets configs parserOptions.ecmaVersion from 2018 to 2020.
• Change supported version of ESLint from 6.0.0 to 6.2.0.
• Upgrade eslint-utils

Rules

• custom-event-name-casing
• no-async-in-computed-properties
• no-deprecated-dollar-listeners-api
• no-deprecated-dollar-scopedslots-api
• no-deprecated-events-api
• no-deprecated-vue-config-keycodes
• no-lifecycle-after-await
• no-multiple-slot-args
• no-mutating-props
• no-ref-as-operand
• no-setup-props-destructure
• no-side-effects-in-computed-properties
• no-unused-properties
• no-watch-after-await
• order-in-components
• require-default-prop
• require-explicit-emits
• require-slots-as-functions
• require-valid-default-prop
• this-in-template
• v-on-function-call
• valid-v-bind-sync
• valid-v-model