Fix compilation with ts-node

ts-node by default does not respect the `files` setting in `tsconfig.json`
and therefore does not respect the d.ts file under `types/`.

This commit adds an explicit `typeRoots` option, as recommended by
https://github.com/TypeStrong/ts-node#help-my-types-are-missing

Fixes #989

Signed-off-by: Philip Molares <philip.molares@udo.edu>

tsconfig.json

@@ -10,6 +10,10 @@
     "sourceMap": true,
     "outDir": "./dist",
     "baseUrl": "./",
-    "incremental": true
+    "incremental": true,
+    "typeRoots": [
+      "./types",
+      "./node_modules/@types"
+    ]
   }
 }