nassh 0.8.18.2: Update to hterm 1.4.

* Update to hterm 1.4.
* Modify ./bin/mkzip.sh to warn if nassh_deps.concat.js is not current.

BUG=None
TEST=Manual: edit hterm changelog and ensure that warning appears

Change-Id: Icafc6f4e194a0e6ac54529337cb677f1f43443db
Reviewed-on: https://gerrit.chromium.org/gerrit/48253
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Tested-by: Robert Ginda <rginda@chromium.org>
Commit-Queue: Robert Ginda <rginda@chromium.org>

• nassh/bin/mkzip.sh[diff]
• nassh/doc/changelog.txt[diff]
• nassh/js/nassh_command_instance.js[diff]
• nassh/manifest.json[diff]