Update requirements to Go 1.13

developer/setup.md

@@ -4,7 +4,7 @@ Ready to hack on your site? Here's a quick overview.
 
 ## Prerequisites
 
-* [Go 1.10+](https://golang.org/dl/)
+* [Go 1.13+](https://golang.org/dl/)
 * [Node.js](https://nodejs.org/en/download/)
 
 ## Setting up
@@ -16,9 +16,6 @@ go get -d github.com/writeas/writefreely/cmd/writefreely
 
 cd $GOPATH/src/github.com/writeas/writefreely
 
-# If running Go 1.11+
-export GO111MODULE=on
-
 make build   # Compile the application
 make install # Config, generate keys, setup database, install LESS compiler
 make run     # Run the application