fix typescript: make sourcemaps default on (sveltejs#286)

Author: milahu

src/transformers/typescript.ts

@@ -62,6 +62,7 @@ const transformer: Transformer<Options.Typescript> = ({
   const compilerOptionsJSON = {
     moduleResolution: 'node',
     target: 'es6',
+    sourceMap: true, // generate sourcemap + attach '\n//# source'+'MappingURL=Component.svelte.js.map' to result.code
   };
 
   let basePath = process.cwd();