[ISSUE #9794] Change JDK prerequisite from 1.7+ to 1.8+ in documentation (#9795)

Author: yx9o

BUILDING

@@ -4,7 +4,7 @@ Build Instructions for Apache RocketMQ
 
 (1) Prerequisites
 
-    JDK 1.7+ is required in order to compile and run RocketMQ.
+    JDK 1.8+ is required in order to compile and run RocketMQ.
 
     RocketMQ utilizes Maven as a distribution management and packaging tool. Version 3.0.3 or later is required.
     Maven installation and configuration instructions can be found here: