Make sure to match ask pattern in test_builder

[ono-max]

Current test builder can't get the ask pattern like this. This PR fix it.

$ bin/gentest target.rb
DEBUGGER: Session start (pid: 95363)
[1, 4] in ~/workspace/debug/target.rb
=>    1| a = 1
      2| b = 2
      3| c = 3
      4| d = 4
=>#0	<main> at ~/workspace/debug/target.rb:1
INTERNAL_INFO: {"location":"~/workspace/debug/target.rb:1","line":1}

(rdbg)b 2
 b 2
#0  BP - Line  /Users/naotto/workspace/debug/target.rb:2 (line)
INTERNAL_INFO: {"location":"~/workspace/debug/target.rb:1","line":1}

(rdbg)del
 del
#0  BP - Line  /Users/naotto/workspace/debug/target.rb:2 (line)

# test builder crashed here.