```ruby
class RstudioPreview < Cask
  url 'https://s3.amazonaws.com/rstudio-dailybuilds/RStudio-0.98.752.dmg'
  homepage 'http://www.rstudio.com/ide/download/preview'
  version '0.98.752'
  sha256 '7393ef30b8e49b20e385d0828177400fb91b775e2c078fec7878a43d3a4e5e10'
  link 'RStudio.app'
end
```

Update RStudio preview to 0.98.770
user
```ruby
class RstudioPreview < Cask
  url 'https://s3.amazonaws.com/rstudio-dailybuilds/RStudio-0.98.770.dmg'
  homepage 'http://www.rstudio.com/ide/download/preview'
  version '0.98.770'
  sha256 'f2d9abf1abc624812f93dd2ea17371db89343f3aa1b06740312377302238e041'
  link 'RStudio.app'
end
```
assistant