travis does not use --remote on git submodule update

.gitmodules

@@ -1,6 +1,7 @@
 [submodule "lib/vendor/swiftmailer"]
 	path = lib/vendor/swiftmailer
 	url = https://github.com/swiftmailer/swiftmailer.git
+	branch = 5.x
 [submodule "lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine"]
 	path = lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine
 	url = https://github.com/LExpress/doctrine1.git

.travis.yml

@@ -29,6 +29,8 @@ install:
     - composer self-update
 
 before_script:
+    # by default, --remote is not used on travis
+    - git submodule update --remote --force
     - sh -c 'if [ $(php -r "echo PHP_MINOR_VERSION;") -le 4 ] && [ $(php -r "echo PHP_MAJOR_VERSION;") -le 5 ]; then echo "extension = apc.so" >> ~/.phpenv/versions/$(phpenv version-name)/etc/php.ini; fi;'
     - composer install