Add scalriform preference: placeScaladocAsterisksBeneathSecondAsterisk

Noticed this one was missing. Allows you to prefer the following style:

```scala
/** This is a first line of documentation
  * This is the second line, with asterisk aligned to second asterisk of first line
  */
```

In `~/.sbt/0.13/global.sbt`:

```scala
ensimeConfig := sexp(                                                                                                                                                                   
  key(":compiler-args"), sexp("-Ywarn-dead-code", "-Ywarn-shadowing"),                                                                                                                  
  key(":formatting-prefs"),                                                                                                                                                             
  sexp(                                                                                                                                       
    key(":multilineScaladocCommentsStartOnFirstLine"), true,                                                                                                                            
    key(":placeScaladocAsterisksBeneathSecondAsterisk"), true)                                                                                                                          
)
```