add shell_sort

[gyj963]

hello,I add a shellSort into sort,I hope can contribute to this project. : )

[felipernb]

Hi, could you please fix the linting errors? (https://travis-ci.org/felipernb/algorithms.js/builds/32082065)

You can check it locally by runing make on your machine before committing.

[coveralls]

Coverage remained the same when pulling 072377e on gyj963:master into a4b8d5b on felipernb:master.

[gyj963]

Sorry I did't notice this problem .Thank you for your remind.This is my first time to contribute to project, many things I don't understand . Can I ask a question?
When I running make , there are some errors , I don't know how to fix these... Like this:

D:\repositories\algorithms.js>make
npm install
jshint algorithms data_structures test util
istanbul cover ./node_modules/.bin/_mocha -- -R spec --recursive test

D:\repositories\algorithms.js\node_modules.bin_mocha:2
basedir=dirname "$0"
^
No coverage information was collected, exit without writing coverage information

SyntaxError: Unexpected token ILLEGAL
at Module._compile (module.js:439:25)
at Module._extensions..js (module.js:474:10)
at Object.Module._extensions..js (C:\Users\Administrator\AppData\Roaming\npm
\node_modules\istanbul\lib\hook.js:102:13)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Function.Module.runMain (module.js:497:10)
at runFn (C:\Users\Administrator\AppData\Roaming\npm\node_modules\istanbul\l
ib\command\common\run-with-cover.js:114:16)
at C:\Users\Administrator\AppData\Roaming\npm\node_modules\istanbul\lib\comm
and\common\run-with-cover.js:232:17
at C:\Users\Administrator\AppData\Roaming\npm\node_modules\istanbul\lib\util
\file-matcher.js:56:16
at C:\Users\Administrator\AppData\Roaming\npm\node_modules\istanbul\lib\util
\file-matcher.js:35:9
make: *** [coverage] Error 8

[felipernb]

Hi, I've merged your commit manually and squashed all commits in a single one. Thanks for the contribution!

Regarding the error, I don't really know what's the problem buut it seems that the code coverage tool doesn't work well with Windows. I'm gonna try to take a look and get back to you :)

[gyj963]

OK ! Thank you . Maybe I need to use linux...

[zzz6519003]

neat! i love test~