Use nyc for coverage report

Fixes #1464

package.json

@@ -21,8 +21,6 @@
     "gulp": "3.9.1",
     "gulp-cli": "^1.2.2",
     "gulp-concat": "^2.6.1",
-    "gulp-coveralls": "^0.1.4",
-    "gulp-istanbul": "^1.1.1",
     "gulp-mocha": "^3.0.1",
     "gulp-sourcemaps": "1.9.1",
     "gulp-typescript": "^3.1.3",
@@ -33,6 +31,7 @@
     "node-pty": "^0.7.2",
     "nodemon": "1.10.2",
     "npm-run-all": "^4.1.2",
+    "nyc": "^11.8.0",
     "sorcery": "^0.10.0",
     "tslint": "^5.9.1",
     "tslint-consistent-codestyle": "^1.13.0",
@@ -50,13 +49,13 @@
     "test": "npm-run-all mocha lint",
     "test-debug": "node --inspect-brk node_modules/.bin/gulp test",
     "test-suite": "gulp mocha-suite --test",
-    "test-coverage": "gulp mocha-coverage",
+    "test-coverage": "nyc -x gulpfile.js -x '**/*test*' npm run mocha",
     "mocha": "gulp test",
     "build:docs": "jsdoc -c jsdoc.json",
     "tsc": "tsc",
     "build": "gulp build",
     "prepublish": "npm run build",
-    "coveralls": "gulp coveralls",
+    "coveralls": "nyc report --reporter=text-lcov | coveralls",
     "webpack": "gulp webpack",
     "watch": "gulp watch"
   }