Describe the bug
History multi-select list contains duplicates.

To Reproduce
Steps to reproduce the behavior:

1. Run

   brew install docker-machine
   brew install docker-config
   brew install docker-config
   brew install docker-machine
   

2. emplace history $HISTFILE

...
  [x] docker-machine (Homebrew)
  [x] docker-config (Homebrew)
  [x] docker-config (Homebrew)
  [x] docker-machine (Homebrew)
...

Expected behavior
Duplicates should be eliminated.

Desktop (please complete the following information):

• OS: mac
• Shell: zsh

Additional context
iirc , docker-config doesnt exist, but that is a separate problem

Machine information

Software version

emplace 1.3.1-alpha.0

Operating system

Darwin 20.3.0

Environment variables

SHELL=/usr/local/bin/zsh
EMPLACE_CONFIG='/Users/john.vandenberg/Library/Application Support/emplace.toml'

Git version

> git --version
git version 2.31.0

Compile time information

• Profile: release
• Target triple: x86_64-apple-darwin
• Family: unix
• OS: macos
• Architecture: x86_64
• Pointer width: 64
• Endian: little
• CPU features: fxsr,sse,sse2,sse3,ssse3
• Host: x86_64-apple-darwin