Fix "spring.mandatory-file-encoding" property doc

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -456,7 +456,7 @@ content into your application; rather pick only the properties that you need.
 	spring.aop.proxy-target-class=
 
 	# FILE ENCODING ({sc-spring-boot}/context/FileEncodingApplicationListener.{sc-ext}[FileEncodingApplicationListener])
-	spring.mandatory-file-encoding=false
+	spring.mandatory-file-encoding= # Expected character encoding the application must use
 
 	# SPRING SOCIAL ({sc-spring-boot-autoconfigure}/social/SocialWebAutoConfiguration.{sc-ext}[SocialWebAutoConfiguration])
 	spring.social.auto-connection-views=true # Set to true for default connection views or false if you provide your own

spring-boot/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -50,7 +50,7 @@
   {
     "name": "spring.mandatory-file-encoding",
     "sourceType": "org.springframework.boot.context.FileEncodingApplicationListener",
-    "type": "java.lang.String",
+    "type": "java.nio.charset.Charset",
     "description": "Expected character encoding the application must use."
   },
   {