do not touch /// in first lines

issue is that in many shells you can use triple slashes `///`, i.e. `///usr/bin/env jbang "$0" "$@" ; exit $?` as a trick to be compatible with both shell scripts and java code.

JDK javadoc linter had this issue too and is now fixed in https://bugs.openjdk.org/browse/JDK-8341907

would be great if google-java-format could honor the same.