Update minimum JDK version in README

Change-Id: I655d896b268e946e3492661b08add0ebac22c6f0
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>
(cherry picked from commit 67da5635a4)

README.md

@@ -72,7 +72,7 @@ Warnings/Caveats
 - Only the timestamp of the index is used by jgit if the index is
   dirty.
 
-- JGit requires at least a Java 7 JDK.
+- JGit requires at least a Java 8 JDK.
 
 - CRLF conversion is performed depending on the core.autocrlf setting,
   however Git for Windows by default stores that setting during