Fixed mkdir problem.

.gitlab-ci.yml

@@ -50,12 +50,11 @@ release:
 doxygen:
   stage: package
   image: alpine
-  cache: []
   script:
     - apk update && apk add doxygen graphviz ttf-freefont
     - pwd
     - ls -l
-    - mkdir target
+    - mkdir -p target
     - mkdir target/doxygen
     - doxygen src/main/doxygen/doxygen.conf
     - mv target/doxygen/html/ public/
@@ -63,4 +62,4 @@ doxygen:
     paths:
       - public
   only:
-    - master
+    - master