Change png/jpg files do not trigger Travis ci

.travis.yml

@@ -42,7 +42,7 @@ addons:
 before_install:
   - |
     if [ ${JOB} == "BUILD_AND_TEST" ]; then
-      if ! git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qvE '(\.md$)|(\.rst$)'
+      if ! git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qvE '(\.md$)|(\.rst$)|(\.jpg$)|(\.png$)'
       then
         echo "Only markdown docs were updated, stopping build process."
         exit