use rxjs/Observable and change http.get error handling

src/http-loader.ts

@@ -1,6 +1,6 @@
 import {HttpClient} from "@angular/common/http";
 import {TranslateLoader} from "@ngx-translate/core";
-import {Observable} from 'rxjs/Rx';
+import {Observable} from 'rxjs/Observable';
 
 export class TranslateHttpLoader implements TranslateLoader {
     loadedTranslations: { [index: string]: Object; } = {};
@@ -27,13 +27,13 @@ export class TranslateHttpLoader implements TranslateLoader {
     public preLoad(lang: string): Promise<any> {
         return new Promise((resolve, reject) => {
                 this.http.get(`${this.prefix}${lang}${this.suffix}`)
-            .catch((error: any): any => {
-                resolve(null);
-            })
-            .subscribe((result) => {
+            .subscribe(
+              result => {
                 this.loadedTranslations[lang] = result;
                 resolve(result);
-            });
+              },
+              error => {resolve(null)}
+            );
         });
     }
 }