make sure it is origin/master

Author: mark-i-m

ci/linkcheck.sh

@@ -5,7 +5,7 @@ if [ "$TRAVIS_EVENT_TYPE" = "cron" ] ; then
 
   echo "Doing full link check."
 else
-  CHANGED_FILES=$(git diff-tree --no-commit-id --name-only -r master..HEAD | tr '\n' ' ')
+  CHANGED_FILES=$(git diff-tree --no-commit-id --name-only -r origin/master..HEAD | tr '\n' ' ')
   FLAGS="-f $CHANGED_FILES"
 
   echo "Checking files changed in master..HEAD: $CHANGED_FILES"