Use Node.js crypto ripemd160 hash if available.

lib/crypto/hash.js

@@ -28,10 +28,19 @@ Hash.sha256sha256 = function(buf) {
 };
 
 Hash.ripemd160 = function(buf) {
+  $.checkArgument(BufferUtil.isBuffer(buf));
+  return crypto.createHash('ripemd160').update(buf).digest();
+};
+
+// Node.js crypto ripemd160 hashes are not supported in a browser
+// We'll replace with a (slower) version that does.
+if (global.window) {
+  Hash.ripemd160 = function(buf) {
     $.checkArgument(BufferUtil.isBuffer(buf));
     var hash = (new hashjs.ripemd160()).update(buf).digest();
     return new Buffer(hash);
-};
+  };
+}
 
 Hash.sha256ripemd160 = function(buf) {
   $.checkArgument(BufferUtil.isBuffer(buf));