This PR fixes autocorrect code for `Style/HashConversion`
to avoid syntax error.

## Before

Autocorrection causes a syntax error.

```console
echo "Hash[].to_h" | bundle exec rubocop --stdin example.rb -A
Inspecting 1 file
F

Offenses:

example.rb:1:1: C: [Corrected] Style/EmptyLiteral: Use hash literal {} instead of Hash[].
Hash[].to_h
^^^^^^
example.rb:1:1: C: [Corrected] Style/FrozenStringLiteralComment: Missing frozen string literal comment.
Hash[].to_h
^
example.rb:1:1: C: [Corrected] Style/HashConversion: Prefer literal hash to Hash[arg1, arg2, ...].
Hash[].to_h
^^^^^^
example.rb:1:8: W: [Corrected] Lint/RedundantTypeConversion: Redundant to_h detected.
Hash[].to_h
^^^^
example.rb:2:3: F: Lint/Syntax: unexpected token tLPAREN2
(Using Ruby 2.7 parser; configure using TargetRubyVersion parameter, under AllCops)
{}()
^

1 file inspected, 5 offenses detected, 4 offenses corrected
====================
# frozen_string_literal: true
{}()
```

## After

No syntax errors.

```console
$ echo "Hash[].to_h" | bundle exec rubocop --stdin example.rb -A
Inspecting 1 file
W

Offenses:

example.rb:1:1: C: [Corrected] Style/EmptyLiteral: Use hash literal {} instead of Hash[].
Hash[].to_h
^^^^^^
example.rb:1:1: C: [Corrected] Style/FrozenStringLiteralComment: Missing frozen string literal comment.
Hash[].to_h
^
example.rb:1:1: C: [Corrected] Style/HashConversion: Prefer literal hash to Hash[arg1, arg2, ...].
Hash[].to_h
^^^^^^
example.rb:1:8: W: [Corrected] Lint/RedundantTypeConversion: Redundant to_h detected.
Hash[].to_h
^^^^
example.rb:2:1: C: [Corrected] Layout/EmptyLineAfterMagicComment: Add an empty line after magic comments.
{}
^

1 file inspected, 5 offenses detected, 5 offenses corrected
====================
# frozen_string_literal: true

{}
```