Update changelog

Author: ajalt

CHANGELOG.md

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+# Changelog
+
+## [Unreleased]
+### Added
+- `defaultLazy` extension for options and arguments
+
+### Changed
+- `main` now prints messages to stderr instead of stdout
+
+### Fixed
+- Parameter help messages are now wrapped more consistently
+
+## [1.2.0] - 2018-05-07
+### Added
+- Default parameter to option().default()
+
+### Changed
+- Treat tokens with unknown prefixes as arguments (this makes it easier
+  to pass in file paths without using `--`).
+
+## [1.1.0] - 2018-04-15
+### Added
+- `List<String>` overloads to `CliktCommand.parse` and `main`
+- `err` parameter to `TermUi.echo`
+- `error` property to `Abort`
+