fixed typo in readme

Author: Lorl0rd

README.md

@@ -5,7 +5,7 @@ This repository contains two main crates:
 * `compiler-builtins`: symbols that the compiler expects to be available at
   link time
 * `libm`: a Rust implementation of C math libraries, used to provide
-  implementations in `ocre`.
+  implementations in `core`.
 
 More details are at [compiler-builtins/README.md](compiler-builtins/README.md)
 and [libm/README.md](libm/README.md).