Use gender neutral pronouns

Closes #2031

docs/blog/private-engines.rst

@@ -13,7 +13,7 @@ Private engines
 To solve this issue private engines were introduced in :pull:`1823`.
 A new option was added to engines named `tokens`. It expects a list
 of strings. If the user making a request presents one of the tokens
-of an engine, he/she is able to access information about the engine
+of an engine, they can access information about the engine
 and make search requests.
 
 Example configuration to restrict access to the Arch Linux Wiki engine:

docs/dev/search_api.rst

@@ -81,7 +81,7 @@ Parameters
   Theme of instance.
 
   Please note, available themes depend on an instance.  It is possible that an
-  instance administrator deleted, created or renamed themes on his/her instance.
+  instance administrator deleted, created or renamed themes on their instance.
   See the available options in the preferences page of the instance.
 
 ``oscar-style`` : default ``logicodev``
@@ -91,7 +91,7 @@ Parameters
   ``oscar``.
 
   Please note, available styles depend on an instance.  It is possible that an
-  instance administrator deleted, created or renamed styles on his/her
+  instance administrator deleted, created or renamed styles on their
   instance. See the available options in the preferences page of the instance.
 
 ``enabled_plugins`` : optional

docs/user/own-instance.rst

@@ -44,9 +44,9 @@ hidden from visited result pages.
 What are the consequences of using public instances?
 ----------------------------------------------------
 
-If someone uses a public instance, he/she has to trust the administrator of that
+If someone uses a public instance, they have to trust the administrator of that
 instance.  This means that the user of the public instance does not know whether
-his/her requests are logged, aggregated and sent or sold to a third party.
+their requests are logged, aggregated and sent or sold to a third party.
 
 Also, public instances without proper protection are more vulnerable to abusing
 the search service, In this case the external service in exchange returns