add changelog for new version

changelog.md

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+- You can now upgrade your Mantil nodes. Download new version of CLI and run mantil upgrade to upgrade node to the same version as CLI.
+- Stage rest endpoints now support GET requests with proper type conversions for your method parameters.
+- Stage lambdas can now be scheduled with cron option through project environment.
+- Functions folder which contained only boilerplate code is now removed and replaced with build folder which gets automatically generated on each deploy.
+- Stage state now contains last deployment info - node version and time of the deployment.
+
+Fixed: Deploy metrics no longer show aggregate values in watch command.
+Fixed: Tests generated by mantil generate command now have proper package names.