Failed to load the css-edit-groups package

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[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.53.0 x64
**Electron**: 6.1.12
**OS**: Unknown Windows version
**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.r (:11:583713)
at addProperty (:14:1423816)
at Array.reduce (:null:null)
at Obj (:14:1423482)
at transformNode (:14:1424856)
at Value (:14:1422730)
at transformNode (:14:1424856)
at addProperty (:14:1423804)
at Array.reduce (:null:null)
at Obj (:14:1423482)
at transformNode (:14:1424856)
at Value (:14:1422730)
at transformNode (:14:1424856)
at Block (:14:1422688)
at transformNode (:14:1424856)
at Object.parse (:14:1424877)
at m (:11:580956)
at c (:11:581162)
at Object.readFileSync (:11:582255)
at :11:3704072
at Array.map (:null:null)
at Package.loadKeymaps (:11:3704060)
at :11:3697514
at Package.measure (:11:3696677)
at Package.load (:11:3697450)
at PackageManager.loadAvailablePackage (:11:382096)
at :11:380519
at Config.transact (:11:332489)
at PackageManager.loadPackages (:11:380457)
at :1:757118
at Function.all (:null:null)
at AtomEnvironment.startEditorWindow (:1:759157)

```

### Commands

```
```

### Non-Core Packages

```
atom-beautify 0.33.4
atom-bootstrap4 1.4.0
atom-css-comb 3.5.1
atom-email-snippets 0.1.0
atom-file-icons 0.7.1
atom-html-templates 0.1.3
atom-html5-boilerplate 0.2.0
atom-i18n 0.24.1
atom-icons 0.2.2
autoclose-html 0.23.0
autoprefixer 4.2.0
busy-signal 2.0.1
color-picker 2.3.0
css-edit-groups 0.4.2
css-grid-snippets 1.1.1
css-snippets 1.1.0
css-spy 0.6.0
double-tag 1.7.0
editor-settings 1.1.3
emmet 2.4.3
flexbox-snippets 0.3.0
goto-definition 1.3.4
highlight-selected 0.17.0
html-head-snippets 0.2.0
html-to-css 0.2.2
HTML2JS 0.2.1
icon-fonts 3.4.0
intentions 1.1.5
language-html5-subtlegradient 0.1.0
linter 3.1.1
linter-csslint 2.0.6
linter-ui-default 2.2.3
minimap 4.35.7
pigments 0.40.6
project-manager 3.3.8
remote-edit 1.9.0
sync-settings 5.1.0
todo-show 2.3.2
vue-template 0.5.0
w3c-validation 0.4.0
```

Start by reproducing the Atom startup failure with css-edit-groups 0.4.2 and inspect the package keymap data implicated by Package.loadKeymaps. Identify where the duplicate 'cmd-l' entry is defined and verify that the package loads without the duplicate-key error.

Written by the indexing model from the issue text.