add deno task coverage command to generate and preview coverage report

Author: bgrins

.gitignore

@@ -5,3 +5,5 @@ Thumbs.db
 node_modules
 .idea
 .vscode
+cov_profile
+cov_profile.lcov

deno.json

@@ -2,6 +2,7 @@
   "tasks": {
     "test": "deno test",
     "dev": "deno test --watch test.js",
+    "coverage": "deno test --coverage=cov_profile && deno coverage cov_profile --lcov --output=cov_profile.lcov && genhtml -o cov_profile/html cov_profile.lcov && open cov_profile/html/TinyColor/mod.js.gcov.html",
     "serve": "deno run --watch --allow-env --allow-net=unpkg.com,0.0.0.0 --allow-read=. demo/server.jsx",
     "test-npm": "npm install --prefix npm && npm test --prefix npm",
     "build": "deno task test && deno run --allow-env --allow-read --allow-write=. build.js && deno task test-npm",