Merge pull request #134 from NikVolf/z-rng

Avoid using rand_os crate (fixes warnings)

librustzcash/src/rustzcash.rs

@@ -27,8 +27,7 @@ use blake2s_simd::Params as Blake2sParams;
 
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 
-use rand_core::RngCore;
-use rand_os::OsRng;
+use rand_core::{OsRng, RngCore};
 use std::io::BufReader;
 
 use libc::{c_char, c_uchar, size_t};