Parsing `-> do it end` in parse.y leaks memory. We can see this in the
Valgrind output:

    56 bytes in 1 blocks are definitely lost in loss record 1 of 6
        at 0x484E0DC: calloc (vg_replace_malloc.c:1675)
        by 0x188970: calloc1 (default.c:1472)
        by 0x188970: rb_gc_impl_calloc (default.c:8208)
        by 0x188970: ruby_xcalloc_body (gc.c:4598)
        by 0x18B8BC: ruby_xcalloc (gc.c:4592)
        by 0x21DCCA70: new_locations_lambda_body (ripper.y:12844)
        by 0x21DCCA70: ripper_yyparse (ripper.y:5194)
        by 0x21DDA521: rb_ruby_ripper_parse0 (ripper.y:15798)