Plugins fail to load when eslint is installed globally

I've authored a plugin [eslint-no-exclusive-tests](https://github.com/tlvince/eslint-no-exclusive-tests) that warns if certain Jasmine methods are used (`ddescribe, iit` etc.)

When eslint is installed globally (as normal), a module loader error is thrown:

``` shell
❯ eslint spec.js

module.js:340
    throw err;
          ^
Error: Cannot find module 'eslint-plugin-no-exclusive-tests'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at /usr/local/lib/node_modules/eslint/lib/cli-engine.js:122:26
    at Array.forEach (native)
    at loadPlugins (/usr/local/lib/node_modules/eslint/lib/cli-engine.js:115:21)
    at processFile (/usr/local/lib/node_modules/eslint/lib/cli-engine.js:151:9)
    at /usr/local/lib/node_modules/eslint/lib/cli-engine.js:222:30
    at walk (/usr/local/lib/node_modules/eslint/lib/util/traverse.js:82:9)
```

As the [docs](http://eslint.org/docs/developer-guide/working-with-plugins.html) say to add eslint as a peerDependency, it gets installed locally to the project. If using the local eslint, the plugin runs as expected:

``` shell
❯ ./node_modules/.bin/eslint spec.js

spec.js
   3:0   error  Unexpected ddescribe                       no-exclusive-tests/no-exclusive-tests
```

`package.json`:

``` json
...
  "devDependencies": {
    "eslint": "^0.8.0",
    "eslint-plugin-no-exclusive-tests": "^0.2.0"
...
```

`.eslintrc`

``` yaml
plugins:
  - no-exclusive-tests
rules:
  no-exclusive-tests/no-exclusive-tests: 2
```

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