Spatial4j 0.7 was released late December 2017, principally with support for JTS 1.15. There are some other changes less pertinent to Lucene/Solr but I'll refer to the change list:
This JTS release has an API breakage in that the package root was changed from com.vividsolutions to org.locationtech but should otherwise be compatible. JTS is now dual-licensed as EPL 1.0 and EDL 1.0 (a BSD style 3-clause license). This JTS release also included various improvements, including faster LineString intersection. That performance improvement was found in the context of Lucene spatial-extras real-world use.
Anyone using JTS with lucene-spatial-extras will be forced to update to JTS 1.15. I'd like to add a test dependency from lucene-spatial-extras to JTS (the BSD licensed version of course) as there is at least one test with a JUnit "assumeTrue" on it being on the classpath – JtsPolygonTest.