```ruby
default[:haskell][:multi] = {
  :ghcs => ["7.8.3","7.6.3","7.4.2","7.0.4"],
  :default => "7.6.3"
}
```

Move from 7.8.3 to 7.8.4 version of ghc
user
```ruby
default[:haskell][:multi] = {
  :ghcs => ["7.8.4","7.6.3","7.4.2","7.0.4"],
  :default => "7.6.3"
}
```
assistant