[completion] Fixed autocomplete issue when using aliases (#500)

Right now if we try to use tab-complete with an alias, we get the following error (reproduced on a macOS and zsh):

   unrecognized modifier `i'

---------

Co-authored-by: AJ Alt <ajalt@users.noreply.github.com>

CHANGELOG.md

@@ -6,6 +6,7 @@
 - Added `Context.registerClosable` and `Context.callOnClose` to allow you to register cleanup actions that will be called when the command exits. ([#395](https://github.com/ajalt/clikt/issues/395))
 
 ### Fixed
+- Fixed `unrecognized modifier 'i'` that happened on tab-completion when using sub command aliases ([#500](https://github.com/ajalt/clikt/pull/500))
 - Make sure auto complete script works on zsh, fixing the error `complete:13: command not found: compdef` ([#499](https://github.com/ajalt/clikt/pull/499))
 
 ## 4.2.2

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/completion/BashCompletionGenerator.kt

@@ -137,7 +137,7 @@ internal object BashCompletionGenerator {
                     """
                 |      $name)
                 |        (( i = i + 1 ))
-                |        COMP_WORDS=( "${'$'}{COMP_WORDS[@]:0:i}"
+                |        COMP_WORDS=( "${'$'}{COMP_WORDS[@]:0:${'$'}{i}}"
                 """.trimMargin()
                 )
                 toks.joinTo(this, " ", prefix = " ") { "'$it'" }