Add CI step to verify merged vendor js

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

.drone.yml

     when:
       matrix:
         TESTS: check-autoloader
+  check-mergejs:
+    image: nextcloudci/php7.0:php7.0-7
+    commands:
+      - bash ./build/mergejschecker.sh
+    when:
+      matrix:
+        TESTS: check-mergejs
   app-check-code:
     image: nextcloudci/php7.0:php7.0-7
     commands:
     - TESTS: integration-ldap-features
     - TESTS: jsunit
     - TESTS: check-autoloader
+    - TESTS: check-mergejs
     - TESTS: app-check-code
     - TESTS: syntax-php5.6
     - TESTS: syntax-php7.0

build/mergejschecker.sh

+#!/usr/bin/env bash
+
+#Regenerate the vendors core.js
+echo
+echo "Regenerating core/vendor/core.js"
+
+d=`dirname $(readlink -f $0)`
+
+php $d/mergejs.php
+
+files=`git diff --name-only`
+
+for file in $files
+do
+    if [[ $file == core/vendor/core.js ]]
+    then
+        echo "The merged vendor file is not up to date"
+        echo "Please run: php build/mergejs.php"
+        echo "And commit the result"
+        break
+    fi
+done
+
+echo "Vendor js merged as expected. Carry on"
+exit 0