Update Groovy to 2.5.8

[umayrh]

This is a minimal change required to get pivy-importer
JAR to work with Java 13. Otherwise, we may see errors like:

```
$ java -jar ../etc/pivy-importer-0.12.8-all.jar --repo local-ivy-repo numpy:1.14.5

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedClass$3$1 (file:/../pivy-importer-0.12.8-all.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedClass$3$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Exception in thread "main" java.lang.ClassCastException: class [B cannot be cast to class [C ([B and [C are in module java.base of loader 'bootstrap')
        at groovy.json.internal.FastStringUtils$StringImplementation$1.toCharArray(FastStringUtils.java:90)
        at groovy.json.internal.FastStringUtils.toCharArray(FastStringUtils.java:175)
        at groovy.json.internal.BaseJsonParser.parse(BaseJsonParser.java:104)
        at groovy.json.JsonSlurper.parseText(JsonSlurper.java:205)
        at groovy.json.JsonSlurper$parseText.call(Unknown Source)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
        at com.linkedin.python.importer.pypi.PypiApiCache.downloadMetadata(PypiApiCache.groovy:57)
```

[umayrh]

Merge, plz?