Update demo dataset links to point to new endpoint

[gsheni]

• Updated base url for demo datasets

[codecov]

Codecov Report

Merging #3826 (6ae3561) into main (0790687) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #3826   +/-   ##
=====================================
  Coverage   99.7%   99.7%           
=====================================
  Files        343     343           
  Lines      35807   35807           
=====================================
  Hits       35670   35670           
  Misses       137     137           

Impacted Files	Coverage Δ
evalml/demos/breast_cancer.py	100.0% <ø> (ø)
evalml/demos/churn.py	100.0% <ø> (ø)
evalml/demos/diabetes.py	100.0% <ø> (ø)
evalml/demos/fraud.py	100.0% <ø> (ø)
evalml/demos/weather.py	100.0% <ø> (ø)
evalml/demos/wine.py	100.0% <ø> (ø)
evalml/tests/conftest.py	98.0% <ø> (ø)
evalml/tests/demo_tests/test_datasets.py	100.0% <100.0%> (ø)

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