Update pt_testcase: stabby lambda, zero args

Updates pt_testcase to reflect a change in how a stabby lambda
with zero args is parsed.

seattlerb/ruby_parser#189

lib/pt_testcase.rb

@@ -359,7 +359,7 @@ def self.unsupported_tests *tests
   add_19edgecases("lambda { || (x + 1) }",
                   s(:iter,
                     s(:call, nil, :lambda),
-                    0,
+                    s(:args),
                     s(:call, s(:call, nil, :x), :+, s(:lit, 1))),
                   "stabby_args_0"                 => "->() { (x + 1) }",
                   "stabby_args_0_doend"           => "->() do (x + 1) end",