minor #15173 [2.8] Fix lowest deps (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[2.8] Fix lowest deps

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Looks like that by testing the lowest deps on 5.3, we missed some constraints in our test suite.

Commits
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a036a77 [2.8] Fix lowest deps

.travis.yml

@@ -14,7 +14,7 @@ matrix:
         - php: 5.4
         - php: 5.5
         - php: 5.6
-        - php: 5.3
+        - php: 5.6
           env: deps=low
         - php: 5.6
           env: deps=high

src/Symfony/Bundle/FrameworkBundle/composer.json

@@ -20,11 +20,11 @@
         "symfony/asset": "~2.7|~3.0.0",
         "symfony/dependency-injection" : "~2.8",
         "symfony/config" : "~2.4",
-        "symfony/event-dispatcher": "~2.5|~3.0.0",
+        "symfony/event-dispatcher": "~2.8|~3.0.0",
         "symfony/http-foundation": "~2.4.9|~2.5,>=2.5.4|~3.0.0",
         "symfony/http-kernel": "~2.7|~3.0.0",
         "symfony/filesystem": "~2.3|~3.0.0",
-        "symfony/routing": "~2.6,>2.6.4|~3.0.0",
+        "symfony/routing": "~2.8|~3.0.0",
         "symfony/security-core": "~2.6|~3.0.0",
         "symfony/security-csrf": "~2.6|~3.0.0",
         "symfony/stopwatch": "~2.3|~3.0.0",

src/Symfony/Bundle/SecurityBundle/composer.json

@@ -23,6 +23,7 @@
     "require-dev": {
         "symfony/phpunit-bridge": "~2.7|~3.0.0",
         "symfony/browser-kit": "~2.4|~3.0.0",
+        "symfony/config": "~2.8|~3.0.0",
         "symfony/console": "~2.7|~3.0.0",
         "symfony/css-selector": "~2.0,>=2.0.5|~3.0.0",
         "symfony/dependency-injection": "~2.6,>=2.6.6|~3.0.0",