minor #9803 Added a minor note about Composer's plaform config (javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Added a minor note about Composer's plaform config

This is an alternative to #8278 ... we don't create a new article for this ... but we mention this problem and its solution because it's too common to ignore it.

Commits
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e61c5be Added a minor note about Composer's plaform config

Author: javiereguiluz

setup/_update_dep_errors.rst.inc

@@ -19,3 +19,11 @@ the issue.
 
 Or, you may have deeper issues where different libraries depend on conflicting
 versions of other libraries. Check your error message to debug.
+
+Another issue that may happen is that the project dependencies can be installed
+in your local computer but not on the remote server. This usually happens when
+the PHP versions are different on each machine. The solution is to add the
+`platform`_ config option in your `composer.json` file to define the highest
+PHP version allowed for the dependencies (set it to server's PHP version).
+
+.. _`platform`: https://getcomposer.org/doc/06-config.md#platform