http4s needs sbt 1.2

Author: SethTisue

configs/community.dbuild

@@ -2418,6 +2418,9 @@ build += {
   ${vars.base} {
     name: "http4s"
     uri:  ${vars.uris.http4s-uri}
+    // compilation failure on sbt 1.3.0-RC3; not investigated
+    // Symbol 'type org.http4s.json4s.jackson.Json4sJacksonInstances' is missing from the classpath.
+    extra.sbt-version: ${vars.sbt-1-2-version}
     extra.commands: ${vars.default-commands} [
       // didn't compile (October 2018), it didn't seem worth investigating, probably a specs2 change
       "set excludeFilter in (Test, unmanagedSources) in tests := HiddenFileFilter || \"UriSpec.scala\""