minor #4162 DX: Drop symfony/lts (keradus)

This PR was squashed before being merged into the 2.12 branch (closes #4162).

Discussion
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DX: Drop symfony/lts

Replaces #4138

Commits
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6b3fc01e DX: Drop symfony/lts

.travis.yml

@@ -64,8 +64,8 @@ jobs:
             php: 7.0
             install:
                 # Composer: enforce given Symfony components version
-                - if [ "$SYMFONY_VERSION" != "" ]; then composer require --no-update symfony/force-lowest:$SYMFONY_VERSION; fi
-                - if [ "$SYMFONY_VERSION" != "" ]; then composer require --no-update symfony/lts:$(echo $SYMFONY_VERSION | grep -o 'v[0-9]\+') || true; fi
+                - if [ "$SYMFONY_VERSION" != "" ]; then composer global show symfony/flex -q || travis_retry composer global require $DEFAULT_COMPOSER_FLAGS symfony/flex; fi
+                - if [ "$SYMFONY_VERSION" != "" ]; then composer config extra.symfony.require $SYMFONY_VERSION || true; fi
 
                 - travis_retry composer update $DEFAULT_COMPOSER_FLAGS $COMPOSER_FLAGS
                 - composer info -D | sort
@@ -83,7 +83,7 @@ jobs:
             <<: *STANDARD_TEST_JOB
             stage: Test
             php: 7.1
-            env: SYMFONY_DEPRECATIONS_HELPER=weak PHP_CS_FIXER_TEST_USE_LEGACY_TOKENIZER=1 SYMFONY_VERSION="v4.0"
+            env: SYMFONY_DEPRECATIONS_HELPER=weak PHP_CS_FIXER_TEST_USE_LEGACY_TOKENIZER=1 SYMFONY_VERSION="~4.1.0"
 
         -
             <<: *STANDARD_TEST_JOB