Re-introduce escaping of tabs.

[jrallison]

I ran into a problem upgrading to the latest version of json_builder. A recent commit refactored String#json_escape, and removed escaping of tabs.

The result:

irb> val = "a\tb"
=> "a\tb"
irb> j = JSONBuilder::Compiler.generate { v val }
=> "{\"v\": \"a\tb\"}"
irb> JSON.parse j
JSON::ParserError: 757: unexpected token at '{"v": "a   b"}'
    from /Users/jrallison/.rbenv/versions/1.9.3-p194-perf/gemsets/customerio/gems/json_pure-1.7.4/lib/json/common.rb:155:in `parse'
    from /Users/jrallison/.rbenv/versions/1.9.3-p194-perf/gemsets/customerio/gems/json_pure-1.7.4/lib/json/common.rb:155:in `parse'
    from (irb):6
    from /Users/jrallison/.rbenv/versions/1.9.3-p194-perf/gemsets/customerio/gems/railties-3.2.2/lib/rails/commands/console.rb:47:in `start'
    from /Users/jrallison/.rbenv/versions/1.9.3-p194-perf/gemsets/customerio/gems/railties-3.2.2/lib/rails/commands/console.rb:8:in `start'
    from /Users/jrallison/.rbenv/versions/1.9.3-p194-perf/gemsets/customerio/gems/railties-3.2.2/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

This pull request adds back tab escaping.

[travisbot]

This pull request passes (merged 24f89f6b into 1def4d01).

[dewski]

Thanks for fixing this and adding a test as well. :metal: I cut a new release at 3.1.6 for you to use.