correct DataLoader import

Using 
'''typescript
import DataLoader from 'dataloader'
'''
leads to the error: "TypeError: dataloader_1.default is not a constructor"
at the point where the generateDataLoader function is called.

changing to 

'''typescript
import * DataLoader from 'dataloader' 
'''

fixes this issue

Author: schardtbc

README.md

@@ -18,7 +18,7 @@ npm install --save nestjs-dataloader
 We start by implementing the ```NestDataLoader``` interface. This tells ```DataLoader``` how to load our objects.
 
 ``` typescript
-import DataLoader from 'dataloader';
+import * as DataLoader from 'dataloader';
 import { Injectable } from '@nestjs/common';
 import { NestDataLoader } from 'nestjs-dataloader';
 ...
@@ -61,7 +61,7 @@ export class ResolversModule { }
 ### Using the NestDataLoader
 Now that we have a dataloader and our module is aware of it, we need to pass it as a parameter to an endpoint in our graphQL resolver.
 ``` typescript
-import DataLoader from 'dataloader';
+import * as DataLoader from 'dataloader';
 import { Loader } from 'nestjs-dataloader';
 ...
 
@@ -78,4 +78,4 @@ export class AccountResolver {
 ```
 The important thing to note is that the parameter of the ```@Loader``` decorator is the name of the ```NestDataLoader``` class we want to be injected to the method. The DataLoader library will handle bulk retrieval and caching of our requests. Note that the caching is stored on a per-request basis.
 ## Contributing
-Pull requests are always welcome. For major changes, please open an issue first to discuss what you would like to change.
+Pull requests are always welcome. For major changes, please open an issue first to discuss what you would like to change.