parser: funcall argument parsing bug

[i4ki]

When adding tests for #213 I found a parser bug in the funcall arguments.
See below:

λ> fn func(a) { echo $a }
λ> func("a" "b")
ERROR: Wrong number of arguments for function func. Expected 1 but found 2

The comma seems optional, but this is not a feature hehe
I'll address this issue in #213 also.