Make travis/jenkins check for lint on files which are clean to start with

scripts/travis.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -ex
+
+npm run test
+./.travis-test-riot.sh
+
+# run the linter, but exclude any files known to have errors or warnings.
+./node_modules/.bin/eslint --max-warnings 0 \
+    --ignore-path .eslintignore.errorfiles \
+    src test