Add pandoc install in pandoc CI

.gitlab-ci.yml

@@ -71,6 +71,9 @@ doc_build:
   - navipy_install
   - coverage
 
+  before_script:
+  - apt-get install -y -qq pandoc
+
   script:
   - source $CI_PROJECT_DIR/venv/bin/activate
   - cd doc ; make html
@@ -79,4 +82,4 @@ doc_build:
     paths:
     - doc/build
     
-    expire_in: 1 week
\ No newline at end of file
+    expire_in: 1 week