diff -r 7a30a3cc2763 -r 9096895dc2a6 lib/browser/build
--- a/lib/browser/build	Fri Apr 20 11:41:09 2018 +0200
+++ b/lib/browser/build	Fri Apr 20 11:44:09 2018 +0200
@@ -63,7 +63,7 @@
 
   rm -rf classes && mkdir classes
 
-  isabelle_jdk javac -d classes -source 1.4 "${SOURCES[@]}" || \
+  isabelle_jdk javac -d classes -source 1.6 "${SOURCES[@]}" || \
     fail "Failed to compile sources"
   isabelle_jdk jar cf "$(platform_path "$TARGET")" -C classes . ||
     fail "Failed to produce $TARGET"