Add nyc and codecov for code coverage

Author: wooorm

.gitignore

@@ -1 +1,3 @@
-/node_modules/
+.nyc_output/
+coverage/
+node_modules/

.prettierignore

@@ -0,0 +1 @@
+coverage/

.travis.yml

@@ -2,3 +2,4 @@ language: node_js
 node_js:
   - lts/boron
   - node
+after_script: bash <(curl -s https://codecov.io/bash)

package.json

@@ -30,6 +30,7 @@
     "unist-util-is": "^2.0.0"
   },
   "devDependencies": {
+    "nyc": "^12.0.1",
     "prettier": "^1.13.3",
     "remark-cli": "^5.0.0",
     "remark-preset-wooorm": "^4.0.0",
@@ -39,8 +40,15 @@
   },
   "scripts": {
     "format": "remark . -qfo && prettier --write '**/*.js' && xo --fix",
-    "test": "node test",
-    "cov": "nyc --reporter lcov tape test.js"
+    "test-api": "node test",
+    "test-coverage": "nyc --reporter lcov tape test.js",
+    "test": "npm run format && npm run test-coverage"
+  },
+  "nyc": {
+    "check-coverage": true,
+    "lines": 100,
+    "functions": 100,
+    "branches": 100
   },
   "prettier": {
     "tabWidth": 2,