Update .gitlab-ci.yml file

.gitlab-ci.yml

 image: andykuszyk/latex
 html:
-  - lyx --export xhtml Project1/lyx/main.lyx
+    script:
+      - lyx --export xhtml Project1/lyx/main.lyx
 artifacts:
-  paths:
-    - 'Project1/lyx/main.xhtml'
+    paths:
+      - 'Project1/lyx/main.xhtml'