minor #16553 [ProxyManager] Tmp fix composer reqs issue in ZF (nicolas-grekas)

This PR was submitted for the 2.8 branch but it was merged into the 2.3 branch instead (closes #16553).

Discussion
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[ProxyManager] Tmp fix composer reqs issue in ZF

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

See https://github.com/Ocramius/ProxyManager/issues/260#issuecomment-156962918

Commits
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0125145 [ProxyManager] Tmp fix composer reqs issue in ZF

composer.json

@@ -70,6 +70,7 @@
         "monolog/monolog": "~1.3",
         "propel/propel1": "~1.6",
         "ircmaxell/password-compat": "~1.0",
+        "zendframework/zend-stdlib": "~2.5",
         "ocramius/proxy-manager": "~0.3.1"
     },
     "autoload": {

src/Symfony/Bridge/ProxyManager/composer.json

@@ -18,6 +18,7 @@
     "require": {
         "php": ">=5.3.3",
         "symfony/dependency-injection": "~2.3",
+        "zendframework/zend-stdlib": "~2.5",
         "ocramius/proxy-manager": "~0.3.1"
     },
     "require-dev": {