Fix link to dev.js and prod.js files.

The links on readme.md were pointing to no longer existant files.
With this PR these links are updated to the new location of the
files inside the ./bin directory.

Author: christopher-ramirez

server/readme.md

@@ -1,6 +1,6 @@
 # Server Code
 
-The server provides the API, serves static assets, and renders the pages for Send. The production entrypoint is [prod.js](./prod.js) and the development entrypoint is [dev.js](./dev.js) via `webpack-dev-server`.
+The server provides the API, serves static assets, and renders the pages for Send. The production entrypoint is [prod.js](./bin/prod.js) and the development entrypoint is [dev.js](./bin/dev.js) via `webpack-dev-server`.
 
 ## Server configuration
 
@@ -16,4 +16,4 @@ Contains all the server routes and handlers for the API and pages
 
 ## Storage
 
-Contains implementations of possible storage engines for the files and metadata
+Contains implementations of possible storage engines for the files and metadata