test cases will read expected test data as UTF-8

[Snap252]

so all test cases run under windows insider eclipse and with maven

• before there where two failed test cases:

** Running com.vaadin.sass.testcases.scss.VaadinThemes
Tests run: 2, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 3.578 sec <<< FAILURE! - in com.vaadin.sass.testcases.scss.VaadinThemes
** Tests run: 109, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.964 sec <<< FAILURE! - in com.vaadin.sass.testcases.scss.AutomaticSassTests

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