Add covariance to main method (#197)

Fixes #196

Author: ajalt

CHANGELOG.md

@@ -7,6 +7,7 @@
 ### Changed
 - When `printHelpOnEmptyArgs` is `true` and no arguments are present, or when `invokeWithoutSubcommand` is `false` and no subcommand is present, `CliktCommand.main` will now exit with status code 1 rather than 0. 
 - `restrictTo` now works with any `Comparable` value, not just `Number`.
+- `CliktCommand.main` now accepts `Array<out String>`, not just `Array<String>`.
 
 ### Fixed
 - Fixed option values being reset when calling multiple subcommands with `allowMultipleSubcommands=true` ([#190](https://github.com/ajalt/clikt/issues/190))

clikt/src/commonMain/kotlin/com/github/ajalt/clikt/core/CliktCommand.kt

@@ -295,7 +295,7 @@ abstract class CliktCommand(
         }
     }
 
-    fun main(argv: Array<String>) = main(argv.asList())
+    fun main(argv: Array<out String>) = main(argv.asList())
 
     /**
      * Perform actions after parsing is complete and this command is invoked.