Change to scikit-learn from sklearn

This pull request is to update to version 2.6.0 for TabPy.
It will include these improvements:

Fixes deprecation of sklearn in favor of current package name scikit-learn

It will include these breaking changes:

n/a

TabPy support for Python 3.9

Improvements

• A server with Adhoc Disabled Flag on with the wrong credentials will now
  return wrong credentials error instead of telling the user
  that Adhoc Scripts are not allowed on this server.
• Added documentation for how to run TabPy projects with local changes

Breaking changes

• Discontinued support for Python 3.6
• Added support for Python 3.9

Add toggle to turn off evaluate API

v2.4.0

Improvements

• Add toggle to turn off evaluate API.

Breaking changes

• Changing error code to 406 when server not configured for authentication
  but credentials are provided by client.

Add test files to .tar.gz and .zip releases

v2.3.2

Improvements

• Add test files to .tar.gz and .zip releases.

Fixed deployed functions overriding

Bug fixes

• Overriding deployed models.

Improvements

• Fixed scrutinizer test run failure.

Auth Bug Fix

v2.2.0

Breaking changes

• TabPy fails with 400 when it is not configure for authentication
  but credentials are provided by client.

Bug fixes

• When TabPy is running with no console attached it is not failing
  with 500 when trying to respond with 401 status.
• tabpy.query() failing when auth is configured.

Improvements

• Minor code cleanup.

v 1.1.0: Securing /info with auth

Improvements

• Authorization is now required for the /info API method.
  This method did not check authentication previously. This change is
  backwards compatible with Tableau clients.

• Improved config parsing flexibility. Previously the
  TABPY_EVALUATE_TIMEOUT setting would be set to a default if
  tabpy couldn't parse the value. Now it will throw an exception
  at startup.

TabPy v1.0.0: Tableau Supported now!

Improvements

• Minor: feature name changed to analytics extensions.
• Startup script files deleted.
• Index page updated.

Other

• TabPy is now Tableau Supported (used to be Community Supported).

v0.9.0: Fix model deployment with removing usage of pip._internal

Improvements

• Models deployment doesn't depend on pip._internal anymore.
• Package size reduced.

v 0.8.13: Python 3.8 support

Improvements

• TabPy works with Python 3.8 now.
• Documentation updates with referencing Tableau Help pages.
• Added Client.remove() method for deleting deployed models.

Bug Fixes

• Fixed failing Ctrl+C handler.
• Fixed query_timeout bug.
• Fixed None in result collection bug.
• Fixed script evaluation with missing result/return bug.
• Fixed startup failure on Windows for Python 3.8.
• Fixed bug for NaN in returned result collection.
• Fixed bug for None as a result of a script.