Fix minor typo: succesful --> successful

Author: gasi

servant-client/CHANGELOG.md

@@ -6,7 +6,7 @@ HEAD
 * Added support for `path` on `BaseUrl`.
 * `client` now takes an explicit `Manager` argument.
 * Use `http-api-data` instead of `Servant.Common.Text`
-* Client functions now consider any 2xx succesful.
+* Client functions now consider any 2xx successful.
 * Remove matrix params.
 
 0.4.1