GUI: Removed unused gulp package

Change-Id: I8c766c16d99ba35b2cecc78ab2ef5cf3086d5ddd
diff --git a/tools/gui/gulp-tasks/bundles/unit-tests/index.js b/tools/gui/gulp-tasks/bundles/unit-tests/index.js
index 2d0b903..88b1f75 100644
--- a/tools/gui/gulp-tasks/bundles/unit-tests/index.js
+++ b/tools/gui/gulp-tasks/bundles/unit-tests/index.js
@@ -1,5 +1,4 @@
 import gulp from 'gulp';
-import istanbul from 'gulp-istanbul';
 import path from 'path';
 import { Server } from 'karma';