fix field default values

test/cases/function_definition/function_ops.tst

@@ -9,9 +9,7 @@ s(:expressions,
     s(:parameters,
       s(:parameter, :int, :x)),
     s(:expressions,
-      s(:name, :int),
-      s(:assign,
-        s(:name, :abba),
+      s(:field_def, :int, :abba,
         s(:int, 5)),
       s(:operator, "+",
         s(:name, :abba),

test/cases/function_definition/function_return.tst

@@ -9,9 +9,7 @@ s(:expressions,
     s(:parameters,
       s(:parameter, :ref, :n)),
     s(:expressions,
-      s(:name, :int),
-      s(:assign,
-        s(:name, :i),
+      s(:field_def, :int, :i,
         s(:field_access,
           s(:receiver,
             s(:name, :n)),