Add setting channel overwrites

src/client/ClientDataResolver.js

@@ -38,7 +38,7 @@ class ClientDataResolver {
     if (user instanceof User) {
       return user;
     } else if ($string(user)) {
-      return this.client.users.get(user.id);
+      return this.client.users.get(user);
     } else if (user instanceof Message) {
       return user.author;
     } else if (user instanceof Guild) {

src/client/rest/RESTMethods.js

@@ -284,6 +284,14 @@ class RESTMethods {
     });
   }
 
+  setChannelOverwrite(channel, payload) {
+    return new Promise((resolve, reject) => {
+      this.rest.makeRequest('put', `${Constants.Endpoints.channelPermissions(channel.id)}/${payload.id}`, true, payload)
+        .then(resolve)
+        .catch(reject);
+    });
+  }
+
   updateGuildRole(role, _data) {
     return new Promise((resolve, reject) => {
       /*