upgrade to sbt 1.4.0-RC1 (#364)

SethTisue · web-flow · commit ec7cdd4cf705 · 2020-09-08T19:03:10.000-07:00
I'd like to dogfood this release to make sure that we're still
able to publish our modules with it
diff --git a/project/build.properties b/project/build.properties
@@ -1 +1 @@
-sbt.version=1.3.13
+sbt.version=1.4.0-RC1
