Fix name of C function

The name of the generichash function was wrong, so it was not possible to find it when
loading the NIF.

c_src/hash.c

@@ -4,7 +4,7 @@
 
 #include "hash.h"
 
-ERL_NIF_TERM enacl_crypto_hash_nif(ErlNifEnv *env, int argc,
+ERL_NIF_TERM enacl_crypto_hash(ErlNifEnv *env, int argc,
                                ERL_NIF_TERM const argv[]) {
   ErlNifBinary input;
   ErlNifBinary result;