minor #8820 Update web_server_configuration.rst (sundayglee)

This PR was submitted for the 3.4 branch but it was merged into the 2.7 branch instead (closes #8820).

Discussion
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Update web_server_configuration.rst

On Ubuntu 16.04, the location of php7.1 fpm socket is at /run/php/php7.1-fpm.sock and not on /var/run/php7.1-fpm.sock

Commits
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6fbf9ca Update web_server_configuration.rst

Author: xabbuh

setup/web_server_configuration.rst

@@ -274,7 +274,7 @@ The **minimum configuration** to get your application running under Nginx is:
         # This rule should only be placed on your development environment
         # In production, don't include this and don't deploy app_dev.php or config.php
         location ~ ^/(app_dev|config)\.php(/|$) {
-            fastcgi_pass unix:/var/run/php7.1-fpm.sock;
+            fastcgi_pass unix:/run/php/php7.1-fpm.sock;
             fastcgi_split_path_info ^(.+\.php)(/.*)$;
             include fastcgi_params;
             # When you are using symlinks to link the document root to the
@@ -289,7 +289,7 @@ The **minimum configuration** to get your application running under Nginx is:
         }
         # PROD
         location ~ ^/app\.php(/|$) {
-            fastcgi_pass unix:/var/run/php7.1-fpm.sock;
+            fastcgi_pass unix:/run/php/php7.1-fpm.sock;
             fastcgi_split_path_info ^(.+\.php)(/.*)$;
             include fastcgi_params;
             # When you are using symlinks to link the document root to the