minor symfony#9072 Using --dev to install the profiler (weaverryan)

This PR was merged into the 4.0 branch.

Discussion
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Using --dev to install the profiler

Let's use `--dev`! :)

Commits
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79e03d8 Update profiler.rst

Author: javiereguiluz

profiler.rst

@@ -12,7 +12,7 @@ install the profiler before using it:
 
 .. code-block:: terminal
 
-    $ composer require profiler
+    $ composer require profiler --dev
 
 .. toctree::
     :maxdepth: 1