Update link to jbang in sdkman description

[davsclaus]

When I run sdk list and browse a bit then I see the link to jbang is from earlier days from Max.

                                                             $ sdk install jbake
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JBang (0.109.0)                             http://github.com/maxandersen/jbang/

JBang makes it easy to use Java for scripting. It lets you use a single file for
code and dependency management and allows you to run it directly.