Add single quotes to example.

In XML, both types of quote can be used in attributes without escaping, as long as the attribute itself uses the other quote type. This doesn't work when the string contains both quote types, which is when you'd consider using the verbose syntax.

Author: player-03

_docs/project-files/xml-format/config.md

@@ -101,9 +101,9 @@ A similar syntax is also available for setting [gradle properties](https://docs.
 	<!-- <https://docs.gradle.org/current/userguide/config_gradle.html#sec:configuring_jvm_memory> -->
 	<gradle-properties org.gradle.jvmargs='-Xmx512m "-XX:MaxMetaspaceSize=384m"' />
 
-	<!-- More verbose option to avoid escaping quotes -->
+	<!-- A more verbose option to avoid escaping quotes. -->
 	<gradle-properties>
-		<org.gradle.project.myProperty>hello "world"</org.gradle.project.myProperty>
+		<org.gradle.project.myProperty>'hello' "world"</org.gradle.project.myProperty>
 	</gradle-properties>
 </config:android>
 ```