Chore: enforce minimum code coverage (eslint-community#142)

Author: bmish

.gitignore

@@ -1,5 +1,6 @@
+.idea
+.nyc_output
+.vscode
 node_modules/
 npm-debug.log
-.vscode
-.idea
 yarn.lock

package.json

@@ -11,7 +11,7 @@
     "lint:js": "eslint . --ignore-pattern \"!.*\"",
     "generate-readme-table": "node build/generate-readme-table.js",
     "generate-release": "node-release-script",
-    "test": "mocha tests --recursive"
+    "test": "nyc --all --check-coverage --include lib mocha tests --recursive"
   },
   "files": [
     "lib/"
@@ -32,6 +32,12 @@
   "dependencies": {
     "eslint-utils": "^2.1.0"
   },
+  "nyc": {
+    "branches": 96,
+    "functions": 98,
+    "lines": 98,
+    "statements": 98
+  },
   "devDependencies": {
     "@not-an-aardvark/node-release-script": "^0.1.0",
     "chai": "^4.1.0",
@@ -48,7 +54,8 @@
     "lodash": "^4.17.2",
     "markdownlint-cli": "^0.27.1",
     "mocha": "^7.1.1",
-    "npm-run-all": "^4.1.5"
+    "npm-run-all": "^4.1.5",
+    "nyc": "^15.1.0"
   },
   "peerDependencies": {
     "eslint": "^7.0.0"