Add travis check for omitting dist in development branch

.travis.yml

@@ -2,5 +2,6 @@ language: node_js
 node_js: lts/*
 
 script:
+- bash .travis/omit-dist.sh
 - npm run lint
 - npm run build

.travis/omit-dist.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+if [ $TRAVIS_BRANCH == "develop" ] && $(git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qE "^(demo/)?dist/"); then
+	echo 'Build output ("dist" and "demo/dist") not permitted in develop' >&2
+	exit 1
+fi