Failed to load the css-edit-groups package

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[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.47.0 x64
**Electron**: 5.0.13
**OS**: Microsoft Windows 10 Home
**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 (:11:582859)
at addProperty (:14:1352180)
at Array.reduce (:null:null)
at Obj (:14:1351846)
at transformNode (:14:1353220)
at Value (:14:1351094)
at transformNode (:14:1353220)
at addProperty (:14:1352168)
at Array.reduce (:null:null)
at Obj (:14:1351846)
at transformNode (:14:1353220)
at Value (:14:1351094)
at transformNode (:14:1353220)
at Block (:14:1351052)
at transformNode (:14:1353220)
at Object.parse (:14:1353241)
at m (:11:580102)
at c (:11:580308)
at Object.readFileSync (:11:581401)
at :11:3302898
at Array.map (:null:null)
at Package.loadKeymaps (:11:3302886)
at :11:3296340
at Package.measure (:11:3295535)
at Package.load (:11:3296276)
at PackageManager.loadAvailablePackage (:11:381312)
at :11:379735
at Config.transact (:11:331800)
at PackageManager.loadPackages (:11:379673)
at :1:755624
at Function.all (:null:null)
at AtomEnvironment.startEditorWindow (:1:757663)

```

### Commands

```
```

### Non-Core Packages

```
aligner-css 1.2.1
aligner-javascript 1.3.0
atom-css-clean 2.24.1
atom-css-comb 3.5.1
atom-css-unit-converter 1.1.1
atom-idiomatic-comments-css-snippets 0.1.0
atom-material-syntax 1.0.8
atom-material-ui 2.1.3
autocomplete-javascript 0.0.2
busy-signal 2.0.1
caniuse-css 1.1.5
css-color-name 0.4.0
css-comb 2.5.0
css-declaration-sorter 2.0.0
css-edit-groups 0.4.2
css-from-html 0.1.5
css-grid-snippets 1.1.1
css-helper-snippets 0.3.0
css-hyperclick 0.1.5
css-in-js 1.4.0
css-remap 1.1.5
css-skeleton-maker 0.1.4
css-snippets 1.1.0
css-specificity 0.2.2
css-spy 0.6.0
css-triggers 1.0.2
emmet-jsx-css-modules 1.0.0
es6-javascript 1.0.0
escape-to-javascript-string 0.6.0
export-html 3.1.0
format-javascript-comment 0.2.5
html-head-snippets 0.2.0
html-outliner 0.1.1
html-presets 1.1.2
html-shorcuts-react 3.0.3
html-tab 1.0.2
html-tag-auto-complete 0.1.1
html-template-generator 0.3.0
html-to-css 0.2.2
html-to-elm 0.2.0
html-to-javascript 0.2.0
html-to-jsx 2.0.3
html-wrapper 0.2.0
Hydrogen 2.14.1
ide-css 0.3.4
ide-html 0.6.0
insales-javascript-snippets 0.7.1
intentions 1.1.5
javascript-drag-import 0.1.13
javascript-refactor 0.7.1
javascript-snippets 1.2.1
javascript-standard-snippets 0.2.1
language-javascript-jsx 0.3.7
language-javascript-plus 3.0.2
linter 2.3.1
linter-spell 0.15.0
linter-spell-html 0.7.0
linter-spell-javascript 0.9.0
linter-ui-default 1.8.1
make-html-code 1.4.0
markdown-to-html 0.5.0
materialize-css 0.5.1
modern-javascript-snippets 1.1.0
pretty-html 1.0.0
puddletown-javascript-browser-snippets 1.2.0
puddletown-javascript-node-snippets 1.2.1
puddletown-javascript-snippets 1.2.1
Quick-JavaScript 2.2.0
smart-html-tags 1.2.5
sort-css 0.3.0
teletype 0.13.4
treedbox-atom-javascript 2.10.0
turbo-javascript 1.4.0
zentabs 0.8.9
```

Start by reproducing the failure with css-edit-groups 0.4.2 in Atom 1.47.0 on Windows 10, then trace the package-loading path shown in the stack trace, especially Package.loadKeymaps and the duplicate 'cmd-l' key. The issue is resolved when the package loads without the duplicate-key error; no source file or test is identified in the report.

Written by the indexing model from the issue text.