bump sbt version

SethTisue · SethTisue · commit a95f0e0c2e54 · 2019-01-08T18:47:27.000-08:00
no special reason, just keeping current
diff --git a/project/build.properties b/project/build.properties
@@ -1 +1 @@
-sbt.version=0.13.17
+sbt.version=0.13.18
