Failed to load the css-edit-groups package

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[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.31.2 x64
**Electron**: 2.0.7
**OS**: Mac OS X 10.14
**Thrown From**: [css-edit-groups](https://github.com/ekonstantinidis/css-edit-groups) package 0.4.2

### Stack Trace

Failed to load the css-edit-groups package

```
At Duplicate key 'cmd-l'

Error: Duplicate key 'cmd-l'
at Object.detectDuplicateKeys (:40226:19)
at addProperty (:172778:42)
at Array.reduce (:null:null)
at Obj (:172770:34)
at transformNode (:172846:18)
at Value (:172727:18)
at transformNode (:172846:18)
at addProperty (:172777:21)
at Array.reduce (:null:null)
at Obj (:172770:34)
at transformNode (:172846:18)
at Value (:172727:18)
at transformNode (:172846:18)
at Block (:172724:18)
at transformNode (:172846:18)
at Object.parse (:172852:22)
at parseObject (:39975:29)
at parseContentsSync (:40001:22)
at Object.readFileSync (:40113:20)
at keymaps.getKeymapPaths.map (:75390:20)
at Array.map (:null:null)
at Package.loadKeymaps (:75388:50)
at measure (:75069:20)
at Package.measure (:75024:25)
at Package.load (:75065:16)
at PackageManager.loadAvailablePackage (:26199:16)
at config.transact (:26112:20)
at Config.transact (:22777:20)
at PackageManager.loadPackages (:26110:23)
at loadStatePromise.loadState.then (:1080:27)
at :null:null

```

### Commands

```
```

### Non-Core Packages

```
atom-css-clean 2.24.1
atom-css-comb 3.3.1
atom-django 0.3.2
autocomplete-python 1.10.5
css-declaration-sorter 1.2.0
css-edit-groups 0.4.2
css-grid-snippets 1.1.0
css-snippets 1.1.0
django-templates 0.5.0
html-to-css 0.2.2
language-django 0.1.1
platformio-ide-terminal 2.8.0
sort-css 0.3.0
terminal-plus 0.14.5
```

Start by inspecting the package's keymap configuration and searching for the duplicated cmd-l entry reported in the stack trace. Reproduce with Atom 1.31.2 on macOS 10.14 and confirm the package loads without the duplicate-key error.

Written by the indexing model from the issue text.