Upgrade backend

nicolasstucki · nicolasstucki · commit acde7c882c59 · 2017-10-30T10:18:09.000+01:00
* SI-9315 Desugar string concat to java.lang.StringBuilder ... (cd0211cf0fb755281c7607bf6a172df306b5686f)
* SI-9571 Avoid boxing primitives in string concatenation (cb68d9c1868e9fbb3e58cdfd606274e070db5b31)
diff --git a/scala-backend b/scala-backend
@@ -1 +1 @@
-Subproject commit 83b68e5a1fd80afff7f628e813796f5d81a59cc3
+Subproject commit 9dfe905943d0fc946677f75caf38d10915c185ae
