Fixes typo for migrate option

Author: kamal

README.md

@@ -63,7 +63,7 @@ custom:
     start:
       port: 8000
       inMemory: true
-      migration: true
+      migrate: true
 ```
 
 ##  Migrations: sls dynamodb migrate
@@ -141,4 +141,4 @@ Now your local DynamoDB database will be automatically started before running `s
 * [NPM Registry](https://www.npmjs.com/package/serverless-dynamodb-local)
 
 ## License
-  [MIT](LICENSE)
+  [MIT](LICENSE)