Failed to load the css-edit-groups package

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[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.52.0 x64
**Electron**: 6.1.12
**OS**: macOS 11.0
**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 (/Applications/Atom.app/Contents/Resources/app/static/:11:583386)
at addProperty (/Applications/Atom.app/Contents/Resources/app/static/:14:1377736)
at Array.reduce ()
at Obj (/Applications/Atom.app/Contents/Resources/app/static/:14:1377402)
at transformNode (/Applications/Atom.app/Contents/Resources/app/static/:14:1378776)
at Value (/Applications/Atom.app/Contents/Resources/app/static/:14:1376650)
at transformNode (/Applications/Atom.app/Contents/Resources/app/static/:14:1378776)
at addProperty (/Applications/Atom.app/Contents/Resources/app/static/:14:1377724)
at Array.reduce ()
at Obj (/Applications/Atom.app/Contents/Resources/app/static/:14:1377402)
at transformNode (/Applications/Atom.app/Contents/Resources/app/static/:14:1378776)
at Value (/Applications/Atom.app/Contents/Resources/app/static/:14:1376650)
at transformNode (/Applications/Atom.app/Contents/Resources/app/static/:14:1378776)
at Block (/Applications/Atom.app/Contents/Resources/app/static/:14:1376608)
at transformNode (/Applications/Atom.app/Contents/Resources/app/static/:14:1378776)
at Object.parse (/Applications/Atom.app/Contents/Resources/app/static/:14:1378797)
at m (/Applications/Atom.app/Contents/Resources/app/static/:11:580629)
at c (/Applications/Atom.app/Contents/Resources/app/static/:11:580835)
at Object.readFileSync (/Applications/Atom.app/Contents/Resources/app/static/:11:581928)
at /Applications/Atom.app/Contents/Resources/app/static/:11:3191711
at Array.map ()
at Package.loadKeymaps (/Applications/Atom.app/Contents/Resources/app/static/:11:3191699)
at /Applications/Atom.app/Contents/Resources/app/static/:11:3185153
at Package.measure (/Applications/Atom.app/Contents/Resources/app/static/:11:3184316)
at Package.load (/Applications/Atom.app/Contents/Resources/app/static/:11:3185089)
at PackageManager.loadAvailablePackage (/Applications/Atom.app/Contents/Resources/app/static/:11:381794)
at PackageManager.loadPackage (/Applications/Atom.app/Contents/Resources/app/static/:11:380522)
at PackageManager.activatePackage (/Applications/Atom.app/Contents/Resources/app/static/:11:383094)
at /Applications/Atom.app/Contents/Resources/app/static/:11:915835
at r (/Applications/Atom.app/Contents/Resources/app/static/:11:910441)
at n (/Applications/Atom.app/Contents/Resources/app/static/:14:1088976)
at /Applications/Atom.app/Contents/Resources/app/static/:14:1089130
at Socket. (/Applications/Atom.app/Contents/Resources/app/static/:14:1087732)
at Socket.emit (events.js:205:15)
at Pipe. (net.js:586:12)
```

### Commands

```
2x -6:50.5.0 core:backspace (input.hidden-input)
-4:17.7.0 application:open (atom-workspace.workspace.scrollbars-visible-when-scrolling.theme-one-dark-syntax.theme-one-dark-ui)
```

### Non-Core Packages

```
atom-prettify 0.1.3
codekit-atom-sync 1.0.0
css-edit-groups 0.4.2
```

Start by inspecting the css-edit-groups package's keymap configuration and searching for duplicate `cmd-l` bindings. Reproduce the failure in Atom 1.52.0, then verify that the package loads without the duplicate-key error.

Written by the indexing model from the issue text.