The GCDSpec test class comment document and the class name are inconsistent

The GCDSpec test class comment document:
```
/**
* This is a trivial example of how to run this Specification
* From within sbt use:
* {{{
* testOnly gcd.GcdDecoupledTester
* }}}
* From a terminal shell use:
* {{{
* sbt 'testOnly gcd.GcdDecoupledTester'
* }}}
*/
```
the class `GCDSpec` should be named `GcdDecoupledTester`
or change the comment
`testOnly gcd.GcdDecoupledTester` to `testOnly gcd.GCDSpec`

Locate the GCDSpec test class and read its documentation comment. Make the class name and the documented testOnly target agree, then verify that the documented command targets the intended test.

Written by the indexing model from the issue text.