Fix grammar

Signed-off-by: George Robinson <[email protected]>

docs/configuration.md

@@ -427,7 +427,7 @@ Label matchers match alerts to routes, silences, and inhibition rules.
 
 If this is a new Alertmanager installation, we recommend enabling UTF-8 strict mode before creating an Alertmanager configuration file. You can find instructions on how to enable UTF-8 strict mode [here](#utf-8-strict-mode).
 
-If this is an existing Alertmanager installation, we recommend running the Alertmanager in the default mode called fallback mode before enabling UTF-8 strict mode. In this mode, Alertmanager will log warnings if you need to make any changes to your configuration file before UTF-8 strict mode can be enabled. Alertmanager will make UTF-8 strict mode the default in the next two versions, so it's important to transition as soon as possible.
+If this is an existing Alertmanager installation, we recommend running the Alertmanager in the default mode called fallback mode before enabling UTF-8 strict mode. In this mode, Alertmanager will log a warning if you need to make any changes to your configuration file before UTF-8 strict mode can be enabled. Alertmanager will make UTF-8 strict mode the default in the next two versions, so it's important to transition as soon as possible.
 
 Irrespective of whether an Alertmanager installation is a new or existing installation, you can also use `amtool` to validate that an Alertmanager configuration file is compatible with UTF-8 strict mode before enabling it in Alertmanager server. You do not need a running Alertmanager server to do this. You can find instructions on how to validate an Alertmanager configuration file using `amtool` [here](#verification).