Remove rootDir from example/tsconfig.json

Inclusion was causing TS6059 'rootDir' is expected
to contain all source files error. Suggestion to remove from:
wmonk/create-react-app-typescript#74

Author: jthetzel

example/tsconfig.json

@@ -13,7 +13,6 @@
     "noUnusedLocals": true,
     "outDir": "./dist",
     "removeComments": true,
-    "rootDir": "./src",
     "sourceMap": true,
     "strictNullChecks": true,
     "suppressImplicitAnyIndexErrors": true,
@@ -23,4 +22,4 @@
     "node_modules",
     "static"
   ]
-}
+}