don't transpile tests

package.json

@@ -7,7 +7,7 @@
         "jest": "jest --verbose",
         "rollup": "rollup",
         "rollup-all": "lerna run rollup",
-        "babel": "babel",
+        "babel": "babel --ignore **/__tests__/**",
         "precise-commits": "precise-commits",
         "prettier": "prettier",
         "prettier-all": "prettier --write *.js{,on} packages/*/{,src/,src/*/,src/*/*/}*.js{,on}",