Add specs for differing whitespace tolerance in lambdas in 1.9 and 2.0

In ruby 1.9.3 you're not allowed a space between the -> and () of a lambda:

```
sinjo@hydrophobe:~/projects/rubyspec$ irb
1.9.3-p448 :001 > -> () {}
SyntaxError: (irb):1: syntax error, unexpected tLPAREN_ARG, expecting keyword_do_LAMBDA or tLAMBEG
-> () {}
    ^
        from /home/sinjo/.rvm/rubies/ruby-1.9.3-p448/bin/irb:13:in `<main>'
```

In 2.0.0 you are allowed it:

```
sinjo@hydrophobe:~/projects/rubyspec$ irb
2.0.0-p247 :001 > -> () {}
 => #<Proc:0x00000001316e78@(irb):1 (lambda)> 
```

This patch introduces a spec for each of those versions, to check that behaviour is followed.