Fix istanbul error about the typescript transpiler

package.json

@@ -7,7 +7,7 @@
     "postinstall": "typings install",
     "start": "node index",
     "pretest": "tslint -s node_modules/tslint-stylish -t stylish src/**/*.ts test/**/*.ts",
-    "test": "istanbul cover -x \"**/*.spec.ts\" -e .ts _mocha",
+    "test": "ts-node node_modules/istanbul/lib/cli.js cover -x \"**/*.spec.ts\" -e .ts _mocha",
     "show-coverage": "xdg-open coverage/lcov-report/index.html",
     "doc-api": "raml2html -i specs/blendb-api-v1.raml -o doc/api-v1-reference.html"
   },

test/mocha.opts

@@ -7,5 +7,4 @@
 --slow 300
 --check-leaks
 --globals expect
---compilers ts:ts-node/register
 ./src/**/*.spec.ts