Add support for line merger of double arrows and array tokens

What about
```php
$a = array(
    'aaaaaa' =>    'b',
    'c' =>
    'd',
    'eeeeee' =>    'f',
);
```
?


It should be changed into:
```php
$a = array(
    'aaaaaa' =>    'b',
    'c' => 'd',
    'eeeeee' =>    'f',
);
```