README.md: bump up required cmake to 3.5.1

we started to use cmake 3.5.1 back in 34f1ee78

Signed-off-by: Kefu Chai <kchai@redhat.com>

diff --git a/README.md b/README.md
index 379d2b3874840e8fb5f7a01afc220eeaca7138f8..27ce841d0177d276fae0e0e709d1b4a90ab3cf8f 100644 (file)
--- a/README.md
+++ b/README.md
@@ -51,7 +51,7 @@ suitable for installation we recommend you build deb or rpm packages,
 or refer to the `ceph.spec.in` or `debian/rules` to see which
 configuration options are specified for production builds.
 
-Prerequisite: CMake 2.8.12
+Prerequisite: CMake 3.5.1
 
 Build instructions: