minor #7498 [Requirements] Clarify what are JSON and ctype (alexislefebvre, javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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[Requirements] Clarify what are JSON and ctype

On: http://symfony.com/doc/2.7/reference/requirements.html#required

I found “*JSON needs to be enabled*” and “*ctype needs to be enabled*” ambiguous, the first may be misinterpreted as a browser need and the second as a C dependency.

I added “*extension*” and links to the official PHP documentation.

After the update, these items will look like this:

> - [JSON extension](http://php.net/manual/book.json.php) needs to be enabled
> - [ctype extension](http://php.net/manual/book.ctype.php) needs to be enabled

Commits
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75bc678 Use https URLs when possible
43e45ac [Requirements] Clarify what are JSON and ctype

Author: xabbuh

reference/requirements.rst

@@ -22,8 +22,8 @@ Required
 --------
 
 * PHP needs to be a minimum version of PHP 5.3.9
-* JSON needs to be enabled
-* ctype needs to be enabled
+* `JSON extension`_ needs to be enabled
+* `ctype extension`_ needs to be enabled
 * Your ``php.ini`` needs to have the ``date.timezone`` setting
 
 .. caution::
@@ -57,3 +57,5 @@ you need to have the PDO driver installed for the database server you want
 to use.
 
 .. _`Requirements section of the README`: https://github.com/symfony/symfony/blob/2.7/README.md#requirements
+.. _`JSON extension`: https://php.net/manual/book.json.php
+.. _`ctype extension`: https://php.net/manual/book.ctype.php