fix(table): Fix change det issue with http example (#6169)

* fix(table): Fix change det issue with http example

* Update table-http-example.ts

Author: andrewseguin

src/material-examples/table-http/table-http-example.ts

@@ -68,8 +68,8 @@ export class ExampleHttpDao {
 export class ExampleDataSource extends DataSource<GithubIssue> {
   // The number of issues returned by github matching the query.
   resultsLength = 0;
-  isLoadingResults: boolean;
-  isRateLimitReached: boolean;
+  isLoadingResults = false;
+  isRateLimitReached = false;
 
   constructor(private exampleDatabase: ExampleHttpDao,
               private paginator: MdPaginator,