Fix typo in comment

Closes gh-1596

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration.java

@@ -124,7 +124,7 @@ public class WebMvcAutoConfiguration {
 		return new HiddenHttpMethodFilter();
 	}
 
-	// Defined as a nested config to ensure WebMvcConfigurerAdapter it not read when not
+	// Defined as a nested config to ensure WebMvcConfigurerAdapter is not read when not
 	// on the classpath
 	@Configuration
 	@EnableWebMvc