README: Mention current Fedora

Fedora 23 is out of support, mention current Fedora.

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/README.md b/README.md
index 907b586..ea8a65e 100644
--- a/README.md
+++ b/README.md
@@ -49,7 +49,7 @@
 
 ### Dependencies for *64-bit* Fedora systems
 
-1. Install Fedora 23 64-bit.
+1. Install Fedora 25 64-bit (older Fedora should also work).
 2. Install the packages necessary for the build:
 
         sudo dnf install gcc-c++ flex bison git ctags cscope expat-devel patch \