Set common approvals endpoint as member.

app/assets/javascripts/merge_request_widget/approvals/services/approvals_api.js.es6

@@ -8,27 +8,24 @@
     }
 
     init(mergeRequestEndpoint) {
-      this.baseEndpoint = mergeRequestEndpoint;
+      this.baseEndpoint = `${mergeRequestEndpoint}/approvals`;
       Vue.http.headers.common['X-CSRF-Token'] = $.rails.csrfToken();
     }
 
     fetchApprovals() {
-      const endpoint = `${this.baseEndpoint}/approvals`;
-      return Vue.http.get(endpoint).catch((err) => {
+      return Vue.http.get(this.baseEndpoint).catch((err) => {
         console.error(`Error fetching approvals. ${err}`);
       });
     }
 
     approveMergeRequest() {
-      const endpoint = `${this.baseEndpoint}/approvals`;
-      return Vue.http.post(endpoint).catch((err) => {
+      return Vue.http.post(this.baseEndpoint).catch((err) => {
         console.error(`Error approving merge request. ${err}`);
       });
     }
 
     unapproveMergeRequest() {
-      const endpoint = `${this.baseEndpoint}/approvals`;
-      return Vue.http.delete(endpoint).catch((err) => {
+      return Vue.http.delete(this.baseEndpoint).catch((err) => {
         console.error(`Error unapproving merge request. ${err}`);
       });
     }