Fix crypto deprecations

COUCHDB-2825
diff --git a/src/oauth.erl b/src/oauth.erl
index e75d5fd..56c7f7b 100644
--- a/src/oauth.erl
+++ b/src/oauth.erl
@@ -128,7 +128,7 @@
 
 hmac_sha1_signature(BaseString, Consumer, TokenSecret) ->
   Key = uri_join([consumer_secret(Consumer), TokenSecret]),
-  base64:encode_to_string(crypto:sha_mac(Key, BaseString)).
+  base64:encode_to_string(couch_crypto:hmac(sha, Key, BaseString)).
 
 hmac_sha1_verify(Signature, HttpMethod, URL, Params, Consumer, TokenSecret) ->
   verify_in_constant_time(Signature, hmac_sha1_signature(HttpMethod, URL, Params, Consumer, TokenSecret)).