Allow brew info to be invoked then tty is false

This should fix the following error

```
Error: undefined method `+' for nil:NilClass
/usr/local/Library/Homebrew/cmd/info.rb:141:in `decorate_dependencies'
/usr/local/Library/Homebrew/cmd/info.rb:125:in `info_formula'
/usr/local/Library/Homebrew/cmd/info.rb:123:in `map'
/usr/local/Library/Homebrew/cmd/info.rb:123:in `info_formula'
/usr/local/Library/Homebrew/cmd/info.rb:36:in `print_info'
/usr/local/Library/Homebrew/cmd/info.rb:34:in `each'
/usr/local/Library/Homebrew/cmd/info.rb:34:in `print_info'
/usr/local/Library/Homebrew/cmd/info.rb:17:in `info'
/usr/local/Library/brew.rb:91:in `send'
/usr/local/Library/brew.rb:91
```
when invoking brew info from a shell that does not support tty