Link to spin.umd.js as alternative for those who can't use ES6 modules

Closes #367.

The UMD file is not included in the npm package since it's unnecessary for anyone using a module bundler.

.gitignore

@@ -1,8 +1,8 @@
 /.grunt
 /node_modules
-/package-lock.json
 /site/bundle.js
 /site/spin.css
 /site/spin.js
+/site/spin.umd.js
 /spin.js
 /spin.d.ts

.npmrc

@@ -0,0 +1 @@
+package-lock=false

package.json

@@ -33,11 +33,11 @@
   },
   "devDependencies": {
     "grunt": "^1.0.3",
-    "grunt-contrib-connect": "^1.0.2",
+    "grunt-contrib-connect": "^2.0.0",
     "grunt-contrib-copy": "^1.0.0",
-    "grunt-gh-pages": "^2.0.0",
-    "rollup": "^0.65.0",
-    "typescript": "^3.0.3"
+    "grunt-gh-pages": "^3.1.0",
+    "rollup": "^1.1.2",
+    "typescript": "^3.3.3"
   },
   "dependencies": {}
 }

rollup.config.js

@@ -1,4 +1,12 @@
 export default [
+    {
+        input: 'spin.js',
+        output: {
+            file: 'site/spin.umd.js',
+            format: 'umd',
+            name: 'Spin',
+        },
+    },
     {
         input: 'site/index.js',
         output: {

site/index.html

@@ -141,6 +141,10 @@ <h3>Bundling</h3>
   <a href="https://webpack.js.org/">Webpack</a> or
   <a href="https://rollupjs.org/">Rollup</a> to create a production-ready code bundle.
 </p>
+<p>
+  If for some reason you can't use ES6 modules or a module bundler, download
+  <a href="spin.umd.js">spin.umd.js</a> and save it in your repo.
+</p>
 
 <h3>Manual insertion</h3>
 <p>