fix: VW adjust learning rate for boston data example

[eisber]

What changes are proposed in this pull request?

Update learning rate. @jackgerrits I assume that the defaults maybe changed? Learning rate was 7 and I changed to 0.5 (did a small hyper parameter search).

How is this patch tested?

Compared RMSE

[eisber]

/azp run

[github-actions]

Hey @eisber 👋!
Thank you so much for contributing to our repository 🙌.
Someone from SynapseML Team will be reviewing this pull request soon.

We use semantic commit messages to streamline the release process.
Before your pull request can be merged, you should make sure your first commit and PR title start with a semantic prefix.
This helps us to create release messages and credit you for your hard work!

Examples of commit messages with semantic prefixes:

• fix: Fix LightGBM crashes with empty partitions
• feat: Make HTTP on Spark back-offs configurable
• docs: Update Spark Serving usage
• build: Add codecov support
• perf: improve LightGBM memory usage
• refactor: make python code generation rely on classes
• style: Remove nulls from CNTKModel
• test: Add test coverage for CNTKModel

To test your commit locally, please follow our guild on building from source.
Check out the developer guide for additional guidance on testing your change.

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov-commenter]

Codecov Report

Merging #1853 (646426b) into master (d64563f) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1853      +/-   ##
==========================================
- Coverage   86.86%   86.85%   -0.02%     
==========================================
  Files         299      299              
  Lines       15506    15506              
  Branches      784      784              
==========================================
- Hits        13470    13467       -3     
- Misses       2036     2039       +3     

Impacted Files	Coverage Δ
...crosoft/azure/synapse/ml/io/http/HTTPClients.scala	75.00% <0.00%> (-7.36%)	⬇️
...gnitive/anomaly/MultivariateAnomalyDetection.scala	88.97% <0.00%> (+0.76%)	⬆️

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[eisber]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jackgerrits]

LGTM, sounds like a more reasonable learning rate. I doubt 7 has ever been default