add ci for eslint

.drone.yml

@@ -0,0 +1,9 @@
+---
+kind: pipeline
+name: eslint
+
+steps:
+- name: run
+  image: nextcloudci/eslint:eslint-1
+  commands:
+    - ./run-eslint.sh

.eslintrc.yml

@@ -0,0 +1,3 @@
+env:
+  browser: true
+  amd: true

run-eslint.sh

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+#!/bin/sh
+
+set -e
+
+# used this pull request for reference
+# https://github.com/nextcloud/spreed/pull/48
+ESLINT=$(which eslint || true)
+if [ -z "$ESLINT" ]
+then
+    echo "could not find eslint in $PATH"
+    exit 1
+fi
+
+echo checking scripts with $ESLINT
+find -name "*.js" -print0 | xargs -0 $ESLINT
+
+# use this line to test changes locally
+#find src -name "*.js" -exec sh -c 'npx eslint $1' -- {} \;