Update sbt to 1.3.9 (#42)

scala-steward · web-flow · commit 4757078b392a · 2020-03-31T21:33:31.000+02:00
diff --git a/project/build.properties b/project/build.properties
@@ -1 +1 @@
-sbt.version=1.3.8
+sbt.version=1.3.9
