Address breaking changes in MLJBase 1.0

[ablaom]

This PR needs:

• Replace built-in measures with measures in StatisticalMeasures.jl MLJBase.jl#909 merged, and MLJBase 1.0 released.

In this PR we:

• Address breaking changes caused by migration of measure MLJBase.jl -> StatisticalMeasures.jl
• Make the string representations of metrics on the MLflow service more informative. The value of the first parameter of the metric is now included in the representation.

To do:

• Bump [compat] for MLJBase

[ablaom]

The fail appears to be orthogonal to the PR. See #27 .

Tests pass locally if I manually launch the mlflow service.