Update azure-pipelines.yml for Azure Pipelines

Checking requirements.txt script run.

Author: szul

azure-pipelines.yml

@@ -21,6 +21,7 @@ steps:
 - script: |
  python -m pip install --upgrade pip
  pip install -e ./libraries/botbuilder-community-dialogs-prompts
+ pip install -r ./libraries/botbuilder-community-dialogs-prompts/requirements.txt
  pip install pytest pytest-azurepipelines
  pip install coveralls
  pip install pylint