lib/browser/build

--- a/lib/browser/build	Tue Dec 22 15:49:22 2020 +0100
+++ b/lib/browser/build	Tue Dec 22 23:59:45 2020 +0100
@@ -63,7 +63,7 @@
 
   rm -rf classes && mkdir classes
 
-  isabelle_jdk javac -d classes -source 1.6 "${SOURCES[@]}" || \
+  isabelle_jdk javac -d classes -source 7 "${SOURCES[@]}" || \
     fail "Failed to compile sources"
   isabelle_jdk jar cf "$(platform_path "$TARGET")" -C classes . ||
     fail "Failed to produce $TARGET"