Modify markdown format in changelog file

CHANGELOG.md

@@ -1,9 +1,6 @@
-HEAD
------------
+## 0.4.0 (unreleased)
 
-
-0.3.1
------------
+## 0.3.1
 
 - Adds proper exit code when printing version via -v/--version flag
 - Adds --version and --debug long flag names
@@ -13,8 +10,7 @@ HEAD
 - Adds --pass flag to specify connection password
 - Fixes --ssl flag usage, previous value was hardcoded
 
-0.3.0
------------
+## 0.3.0
 
 - Renamed `make deps` to `make setup` and fix issues with bootstrapping
 - Removed hardcoded url for CSV export, it now detects application host:port
@@ -22,13 +18,13 @@ HEAD
 - Moved table information view to the sidebar
 - Added --listen flag to specify web server port, still defaults to 8080
 
-0.2.0
------------
+## 0.2.0
+
 - Design tweaks
 - Automatically opens browser on OSX systems
 - Adds query explain functionality
 - Adds export to CSV
 
-0.1.0
------------
-- Initial release
+## 0.1.0
+
+- Initial release