Modernize WA version references

[andrewrfreed]

Update to more reasonable & modern default

config.ini.sample ;API version, default is 2019-02-28, specify the version matching your Watson Assistant ;version=

notebook_ws/WA-Testing-Tool-WS-Python-Notebook.ipynb:    "    'version' : '2019-02-28', #; Update the version of API to match your application or test needs\n",
tests/test_run.py:        delete_workspaces(apikey,self.config[WCS_CREDS_SECTION][WCS_BASEURL_ITEM], '2019-02-28',workspace_ids)
tests/test_run.py:        delete_workspaces(apikey,self.config[WCS_CREDS_SECTION][WCS_BASEURL_ITEM],'2019-02-28',workspace_ids)
tests/test_run.py:        delete_workspaces(apikey,self.config[WCS_CREDS_SECTION][WCS_BASEURL_ITEM], '2019-02-28', workspace_ids)
tests/test_workspaceParser.py:        # delete_workspaces(apikey,config[WCS_CREDS_SECTION][WCS_BASEURL_ITEM], '2019-02-28', workspace_ids)
utils/__init__.py:DEFAULT_WA_VERSION = '2019-02-28'

examples/standard-test.md:version=2019-02-28
examples/blind.md:version=2019-02-28
examples/kfold.md:version=2019-02-28