fix README link to .so

Author: gkorland

README.md

@@ -10,5 +10,5 @@ The Rust API for Redis is based on the https://github.com/brandur/redis-cell pro
 2. install redis [(mac)](https://gist.github.com/tomysmile/1b8a321e7c58499ef9f9441b2faa0aa8)
 3. run `cargo build --example hello`
 4. start a redis server with the hello module 
-`redis-server --loadmodule ./target/debug/examples/libhello.dylib`
+`redis-server --loadmodule ./target/debug/examples/libhello.so`
 5. open a redis cli. and run `HELLO.ADD 31 11`.