minor symfony#8046 Fix missing line (mleczakm)

This PR was submitted for the master branch but it was merged into the 3.3 branch instead (closes symfony#8046).

Discussion
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Fix missing line

Fixes missing tabs on code examples

Commits
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d769fe6 Fix missing line

Author: weaverryan

service_container/import.rst

@@ -73,6 +73,7 @@ decided to move some configuration to a new file:
         // ... some services
 
 To import this file, use the ``imports`` key from a file that *is* loaded:
+
 .. configuration-block::
 
     .. code-block:: yaml