Add pathItem call

Author: vivanwin

src/Webflow.js

@@ -208,6 +208,13 @@ export default class Webflow {
     return this.delete(`/collections/${collectionId}/items/${itemId}`, query);
   }
 
+  patchItem({ collectionId, itemId, ...data }, query = {}){
+    if (!collectionId) return Promise.reject(buildRequiredArgError('collectionId'));
+    if (!itemId) return Promise.reject(buildRequiredArgError('itemId'));
+
+    return this.patch(`/collections/${collectionId}/items/${itemId}`, data, query);
+  }
+
   // Images
 
   // TODO