move doc theme install step into script block to allow caching

Author: stefanotorresi

.travis.yml

@@ -89,10 +89,10 @@ install:
 script:
   - if [[ $TEST_COVERAGE == 'true' ]]; then composer test-coverage ; else composer test ; fi
   - if [[ $CHECK_CS == 'true' ]]; then composer cs-check ; fi
+  - if [[ $DEPLOY_DOCS == "true" && "$TRAVIS_TEST_RESULT" == "0" ]]; then travis_retry curl -sSL https://raw.githubusercontent.com/zendframework/zf-mkdoc-theme/master/theme-installer.sh | bash ; fi
 
 after_script:
   - if [[ $TEST_COVERAGE == 'true' ]]; then travis_retry composer upload-coverage ; fi
 
 after_success:
-  - if [[ $DEPLOY_DOCS == "true" ]]; then travis_retry curl -sSL https://raw.githubusercontent.com/zendframework/zf-mkdoc-theme/master/theme-installer.sh | bash ; fi
   - if [[ $DEPLOY_DOCS == "true" ]]; then ./zf-mkdoc-theme/deploy.sh ; fi