remove timestamp from javadoc

... to reduce size of diffs in auto-generated javadoc pushes.
diff --git a/build.xml b/build.xml
index 95bbf1b..b101073 100644
--- a/build.xml
+++ b/build.xml
@@ -196,7 +196,7 @@
              destdir="build/docs/javadoc"
              maxmemory="512M"
              classpathref="javadoc.classpath"
-             additionalparam="-Xdoclint:none"
+             additionalparam="-Xdoclint:none -notimestamp"
              windowtitle="Guice ${new.api} API"
              author="false"
              protected="true">