Update to use rollup.js

Thanks @ljmerza!

src/index.ts

@@ -0,0 +1,41 @@
+import {
+  LitElement,
+  html,
+  customElement,
+  property,
+  CSSResult,
+  TemplateResult,
+  css
+} from "lit-element";
+
+interface BoilerplateConfig {
+  type: string;
+}
+
+@customElement("boilerplate-card")
+class BoilerplateCard extends LitElement {
+  @property() public hass?: any;
+  @property() private _config?: BoilerplateConfig;
+
+  public setConfig(config: BoilerplateConfig): void {
+    if (!this._config) {
+      // TODO Log error
+    }
+
+    this._config = config;
+  }
+
+  protected render(): TemplateResult | void {
+    if (!this._config || !this.hass) {
+      return html``;
+    }
+
+    return html`
+      <div>boilerplate</div>
+    `;
+  }
+
+  static get styles(): CSSResult {
+    return css``;
+  }
+}