Add explicit generic type

This helps Eclipse Luna to find the correct overload method.
Fixes error:

```
The method getAttribute(String, boolean) in the type ILaunchConfiguration 
is not applicable for the arguments (String, ArrayList<Object>)	

LaunchUpdater.java	/net.sf.eclipsefp.haskell.debug.ui/src/net/sf/eclipsefp/haskell/debug/ui/internal/launch	
line 32
```