Fix typo in search settings upgrade instructions (#2531)

Author: enaut

UPGRADING/v0_15.md

@@ -81,7 +81,7 @@ After the upgrade and migration complete, several follow-up steps are required o
 
 - **Update the spam rules**: Download and apply the latest spam rules from the webadmin ``Manage → Maintenance → Update Spam rules``
 
-- **Update search settings**: Review the updated documentation for search settings, as some configuration options have changed.  In particulat, the Elasticsearch backend now uses **different authentication settings** than previous versions.
+- **Update search settings**: Review the updated documentation for search settings, as some configuration options have changed.  In particular, the Elasticsearch backend now uses **different authentication settings** than previous versions.
 
 - **Rebuild search indexes**: All search indexes must be rebuilt to take advantage of the new indexing strategy. This can be done from the webadmin interface ``Manage → Maintenance``.