eslint: Forbid unnecessary path segments in imports.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

.eslintrc.json

@@ -23,6 +23,7 @@
         "import/first": "error",
         "import/newline-after-import": "error",
         "import/no-unresolved": "error",
+        "import/no-useless-path-segments": "error",
         "import/order": [
             "error",
             {

static/js/portico/integrations.js

@@ -1,6 +1,7 @@
 import _ from "lodash";
 
-import blueslip from "./../blueslip";
+import blueslip from "../blueslip";
+
 import * as google_analytics from "./google-analytics";
 import {path_parts} from "./landing-page";