Upgrade nyc and related packages

Closes #48

package.json

@@ -113,7 +113,7 @@
     "bootstrap": "^3.3.7",
     "bootstrap-switch": "^3.3.4",
     "browserify": "^16.2.2",
-    "chai": "^4.1.2",
+    "chai": "^4.2.0",
     "chai-as-promised": "^7.1.1",
     "copy-webpack-plugin": "^4.6.0",
     "coveralls": "^3.0.2",
@@ -138,7 +138,7 @@
     "ncp": "^2.0.0",
     "node-resemble-js": "^0.2.0",
     "npm-run-all": "^4.1.3",
-    "nyc": "^11.8.0",
+    "nyc": "^13.1.0",
     "open": "^0.0.5",
     "postcss-advanced-variables": "^2.3.3",
     "postcss-calc": "^7.0.1",
@@ -157,7 +157,7 @@
     "rollup-plugin-string": "^2.0.2",
     "script-ext-html-webpack-plugin": "^2.1.2",
     "selenium-webdriver": "^3.5.0",
-    "sinon": "^6.1.4",
+    "sinon": "^7.1.1",
     "sinon-chai": "^3.2.0",
     "spin.js": "^4.0.0",
     "string-replace-webpack-plugin": "^0.1.3",