Do not error out of npm install if postinstall fails.

The postinstall script will (rightly) return non-zero if the API
docs cannot be built, but this creates a problem when building a
container (Docker) image. In that case, we expect the postinstall
to fail, as the required files (spec/*) will not have been copied
into the image when `npm install` is run.

By adding an explicit OR clause we allow postinstall to end
gracefully whether or not the API docs have been built.

lib/www/server/package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1",
-    "postinstall": "[[ -e ./node_modules/DOUGAL_ROOT ]] || ln -s .. ./node_modules/DOUGAL_ROOT; redoc-cli bundle ./spec/openapi.yaml -o ./spec/openapi.html"
+    "postinstall": "test -e node_modules/DOUGAL_ROOT || ln -s .. node_modules/DOUGAL_ROOT; test -e spec && test -e spec/openapi.yaml && node_modules/.bin/redoc-cli bundle ./spec/openapi.yaml -o ./spec/openapi.html || echo API documentation not present or failed to compile >/dev/stderr"
   },
   "author": "Aaltronav s.r.o.",
   "license": "UNLICENSED",