Use 2 deploy providers in .travis.yml to handle nightly and tags.

It does not seem to be possible to have only one script launched in
both cases.
Should really fix #245

.travis.yml

@@ -14,11 +14,13 @@ script:
     - "./node_modules/nightwatch/bin/nightwatch -c nightwatch.js --env firefox"
     - pkill node
 deploy:
-    provider: script
-    # This deployment handles 2 different cases :
-    # - the nightly builds (launched by cron)
-    # - the generation of packages for public releases (launched by a tag)
-    # In both cases, we run the same script, but with different command-line arguments
-    script: if [ "${TRAVIS_TAG}aa" = "aa" ]; then CMD_ARGS=""; else CMD_ARGS="-t -v ${TRAVIS_TAG}"; fi && ./scripts/setup_travis_env.sh && DISPLAY=:99.0 ./scripts/create_all_packages.sh $CMD_ARGS
-    on:
-        condition: ( "$TRAVIS_EVENT_TYPE" = "cron" || "${TRAVIS_TAG}bb" != "bb" )
+    - provider: script
+      # Nightly builds (launched by cron)
+      script: ./scripts/setup_travis_env.sh && DISPLAY=:99.0 ./scripts/create_all_packages.sh
+      on:
+          condition: ( "$TRAVIS_EVENT_TYPE" = "cron" )
+    - provider: script
+      # Generation of packages for public releases (launched by a tag)
+      script: ./scripts/setup_travis_env.sh && DISPLAY=:99.0 ./scripts/create_all_packages.sh -t -v ${TRAVIS_TAG}
+      on:
+          tags: true