fix(package): update ts-morph to version 3.1.2

Closes #13

Author: greenkeeper[bot]

package.json

@@ -53,7 +53,7 @@
     "tslint-config-standard": "^8.0.1"
   },
   "dependencies": {
-    "ts-morph": "3.1.0",
+    "ts-morph": "3.1.2",
     "typescript": "3.5.2"
   }
 }