update j2s version of slivka-java-client

[foreveremain]

Need j2s port of this lib - ideally with a javascript test suite to catch j2s transpilation problems like:
TypeError: text.length is not a function
at clazz.eval [as parse$S$java_text_ParsePosition] (swingjs/j2s/java/text/SimpleDateFormat.js:397:51)
at Object.eval [as c$$S$S$S] (swingjs/j2s/uk/ac/dundee/compbio/slivkaclient/SlivkaService.js:154:23)
at Object.Clazz.new_ (https://builds.jalview.org/artifact/JB-GJB18/shared/build-1/JalviewJS-site/swingjs/swingjs2.js:14687:19)
at Object.eval [as getServices$] (swingjs/j2s/uk/ac/dundee/compbio/slivkaclient/SlivkaClient.js:99:18)
at clazz.eval (swingjs/j2s/jalview/ws/slivkaws/SlivkaWSDiscoverer.js:67:17)
at Object.eval [as get$] (swingjs/j2s/jalview/ws/slivkaws/SlivkaWSDiscoverer.js:50:20)
at Object.eval [as run$] (swingjs/j2s/java/util/concurrent/CompletableFuture.js:1706:21)
at Object.eval [as run$] (swingjs/j2s/java/util/concurrent/ThreadPoolExecutor.js:247:20)
at Object.eval [as nextStateIfUnchanged$O$O$I$I] (swingjs/j2s/javajs/async/SwingJSUtils.js:226:33)
at eval (swingjs/j2s/javajs/async/SwingJSUtils.js:218:57)