Update tool package version from 0.1.0b5 to 0.1.0b6 (microsoft#385)

# Description

Update tool package version from 0.1.0b5 to 0.1.0b6 

# All Promptflow Contribution checklist:
- [x] **The pull request does not introduce [breaking changes]**
- [x] **CHANGELOG is updated for new features, bug fixes or other
significant changes.**
- [x] **I have read the [contribution guidelines](../CONTRIBUTING.md).**

## General Guidelines and Best Practices
- [x] Title of the pull request is clear and informative.
- [x] There are a small number of commits, each of which have an
informative message. This means that previously merged commits do not
appear in the history of the PR. For more information on cleaning up the
commits in your PR, [see this
page](https://github.com/Azure/azure-powershell/blob/master/documentation/development-docs/cleaning-up-commits.md).

Co-authored-by: cs_lucky <[email protected]>

src/promptflow-tools/promptflow/version.txt

@@ -1 +1 @@
-VERSION = "0.1.0b5"
+VERSION = "0.1.0b6"