Fix istanbul covering node_modules.

Author: selaux

.istanbul.yml

@@ -0,0 +1,6 @@
+reporting:
+  print: summary
+  reports:
+    - lcov
+    - html
+  dir: ./build/coverage

package.json

@@ -24,7 +24,7 @@
     },
     "scripts": {
         "lint": "eslint .",
-        "unit-test": "istanbul test --dir build/coverage _mocha test -- --recursive --reporter spec",
+        "unit-test": "istanbul test _mocha test -- --recursive --reporter spec",
         "coverage": "npm run unit-test --coverage && npm run report-coverage-html",
         "report-coverage-html": "istanbul report --dir  build/coverage html",
         "test": "npm run lint && npm run coverage",

test/setup.js

@@ -0,0 +1,7 @@
+'use strict';
+
+var sandboxedModule = require('sandboxed-module');
+
+sandboxedModule.configure({
+    sourceTransformersSingleOnly: [ 'istanbul' ]
+});