Fix default MBeanServer bean name in doc

Closes gh-3283

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

@@ -102,7 +102,7 @@
     "name": "spring.jmx.server",
     "type": "java.lang.String",
     "description": "MBeanServer bean name.",
-    "defaultValue": "mBeanServer"
+    "defaultValue": "mbeanServer"
   },
   {
     "name": "spring.jpa.open-in-view",

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

@@ -447,7 +447,7 @@ content into your application; rather pick only the properties that you need.
 	# JMX
 	spring.jmx.default-domain= # JMX domain name
 	spring.jmx.enabled=true # Expose MBeans from Spring
-	spring.jmx.server=mBeanServer # MBeanServer bean name
+	spring.jmx.server=mbeanServer # MBeanServer bean name
 
 	# RABBIT ({sc-spring-boot-autoconfigure}/amqp/RabbitProperties.{sc-ext}[RabbitProperties])
 	spring.rabbitmq.addresses= # connection addresses (e.g. myhost:9999,otherhost:1111)