minor #465 Bump branch alias to 1.2-dev (nicolas-grekas)

This PR was merged into the 1.1-dev branch.

Discussion
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Bump branch alias to 1.2-dev

we made some pretty significant improvements recently, time to bump?

Commits
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9dc7bde Bump branch alias to 1.2-dev

composer.json

@@ -25,7 +25,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "1.1-dev"
+            "dev-master": "1.2-dev"
         },
         "class": "Symfony\\Flex\\Flex"
     }