Added support for the Parameter ExpressionType in SingleParameterLambda

I'm assuming support for the Parameter type should be in place for this method. I was trying to run a ReQL query similar to:
```
r.db('db').table('table')
  .concatMap(function(b) { return b('tags') })
  .groupedMapReduce(
    function(t) { return t }, 
    function() { return 1 }, 
    function(x,y) { return x.add(y) })
```
but was encountering the following exception:
`System.InvalidOperationException : Failed to perform client-side evaluation of expression tree node; often this is caused by refering to a server-side variable in a node that is only supported w/ client-side evaluation` 

I added a test that mimics what I was trying to accomplish. Thanks!