minor swiftmailer#470 Removed Mockery Dev Flag (GrahamCampbell)

This PR was merged into the 5.2-dev branch.

Discussion
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Removed Mockery Dev Flag

Now that mockery 0.9.1 has been released, we no longer need the `@dev` flag as discussed earlier.

Commits
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5472d02 Removed mockery dev flag

Author: fabpot

composer.json

@@ -18,7 +18,7 @@
         "php": ">=5.2.4"
     },
     "require-dev": {
-        "mockery/mockery": "~0.9@dev"
+        "mockery/mockery": "~0.9"
     },
     "autoload": {
         "files": ["lib/swift_required.php"]