Fix CLI command name

[janpieper]

Fixes problem described in #1207 and discussed in https://forum.exercism.org/t/invalid-completion-script-asdf/18526/11

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Before

$ /tmp/exercism-cli/build/exercism | tail -n1
Use "/tmp/exercism-cli/build/exercism [command] --help" for more information about a command.
$ /tmp/exercism-cli/build/exercism completion bash | head -n3
# bash completion V2 for /tmp/exercism-cli/build/exercism     -*- shell-script -*-

__/tmp/exercism-cli/build/exercism_debug()

After

$ /tmp/exercism-cli/build/exercism | tail -n1
Use "exercism [command] --help" for more information about a command.
$ /tmp/exercism-cli/build/exercism completion bash | head -n3
# bash completion V2 for exercism                             -*- shell-script -*-

__exercism_debug()

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