Fix path to tsconfig-plugins-base.json

I didn't read [0]. I just presumed that it was like all other plugins
where you clone under gerrit/plugins and run bazel build plugins/<name>.

[0] https://gerrit.googlesource.com/plugins/owners/+/refs/heads/master/README.md#build-in-gerrit-tree

Change-Id: I4061eeaed16c86381262096cb089a47c0e5c92ee

owners/web/tsconfig.json

diff --git a/owners/web/tsconfig.json b/owners/web/tsconfig.json
index 1ad0ea9..4a70a7d 100644
--- a/owners/web/tsconfig.json
+++ b/owners/web/tsconfig.json
@@ -1,5 +1,5 @@
 {
-  "extends": "../../../tsconfig-plugins-base.json",
+  "extends": "../../tsconfig-plugins-base.json",
   "compilerOptions": {
     "outDir": "../../../.ts-out/plugins/owners", /* overridden by bazel */
     "lib": [