snapcraft add nodejs and npm as build dependencies

When pulling the docker container snapcore/snapcraft
to build the snap, those 2 packages are not present
by default leading to a failure in the snap creation.

Note: it is good to call `apt-get update` before
`snapcraft` or the build will fail.

snapcraft.yaml

@@ -94,6 +94,8 @@ parts:
             - capnproto
             - curl
             - execstack
+            - nodejs
+            - npm
         stage-packages:
             - libfontconfig1
         override-build: |