Version 3 of less causes TypeError: Object [object Object] has no method 'tryLoadPlugin'

[dbdean]

If you run docker-compose build at the moment, npm install pulls in less=3.0.0, and this causes an error upon invoking less:

Step 19/21 : RUN invoke less
 ---> Running in 089ec6915a80
Downloading from pypi -> /srv/nbviewer/notebook-5.0.0.tar.gz
Collecting notebook==5.0.0
  Downloading notebook-5.0.0.tar.gz (11.5MB)
  Saved ./notebook-5.0.0.tar.gz
Successfully downloaded notebook
[TypeError: Object [object Object] has no method 'tryLoadPlugin']
Extract /srv/nbviewer/notebook-5.0.0.tar.gz in None
ERROR: Service 'nbviewer' failed to build: The command '/bin/sh -c invoke less' returned a non-zero code: 1

This appears to be related to a bug in less 3.0.0, where the tryLoadPlugin is not a function: less/less.js#3116

It can be fixed by pinning less to the latest non-3.0.0 release, but hopefully will be fixed in less itself quickly, so I haven't put in a PR for this project just yet, as it may soon be moot (here's hoping)

diff --git a/package.json b/package.json
index 62bcce1..0cdc821 100644
--- a/package.json
+++ b/package.json
@@ -3,7 +3,7 @@
     "watch-less": "./node_modules/.bin/watch 'invoke less' ./nbviewer/static/less"
   },
   "devDependencies": {
-    "less": "*",
+    "less": "2.7.2",
     "less-plugin-autoprefix": "*",
     "less-plugin-clean-css": "*",
     "bower": "*",