ci(travis): add environment var for apidocs php version

Signed-off-by: Domingo Oropeza <doropeza@teclib.com>

.travis.yml

@@ -7,6 +7,7 @@ env:
     - GLPI_SOURCE="https://github.com/glpi-project/glpi"
     - FI_SOURCE="https://github.com/fusioninventory/fusioninventory-for-glpi"
     - CS=7.2
+    - APIDOCS_PHP=7.1
     - DBNAME=glpitest
     - OLDDBNAME=glpiupgradetest
     - AFTER_SUCCESS_BRANCH=9.3/bugfixes
@@ -57,7 +58,7 @@ script:
 after_success:
   # let's update the documentation and locales
   - if [ ${TRAVIS_PHP_VERSION:0:3} == "$CS" ] && [ "$GLPI_BRANCH" = "$AFTER_SUCCESS_BRANCH" ]; then tests/after_success.sh; fi
-  - if [ ${TRAVIS_PHP_VERSION:0:3} == "7.1" ] && [ "$GLPI_BRANCH" = "$AFTER_SUCCESS_BRANCH" ]; then tests/apidocs.sh; fi
+  - if [ ${TRAVIS_PHP_VERSION:0:3} == "$APIDOCS_PHP" ] && [ "$GLPI_BRANCH" = "$AFTER_SUCCESS_BRANCH" ]; then tests/apidocs.sh; fi
 
 cache:
   directories: