CB-14155 fix btest part 2: export npm script

Followup to btest fix in PR #160
diff --git a/package.json b/package.json
index 3f986a9..67b2dde 100644
--- a/package.json
+++ b/package.json
@@ -17,6 +17,7 @@
   "scripts": {
     "eslint": "eslint src test pkg",
     "test": "grunt test && npm run eslint",
+    "btest": "grunt btest && npm run eslint",
     "build": "grunt compile",
     "build-browserify": "grunt compile-browserify"
   },