Prepare changelog for release v1.4.0 (#48)

CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
+## 1.4.0
+### Changed
+- Redact the password from URLs using simple authentication when storing target metadata.
+
+### Fixed
+- Encoding of URL parameter is the annotation/label `prometheus.io/path` is fixed.
+
 ## 1.3.0
 ### Changed
 - Upgrade the Go Telemetry SDK to version 0.2.0 to fix an issue with NaN values.