fix doc error in fd 3 redirect-and-close example

Fixes documentation error regarding https://github.com/bats-core/bats-core#file-descriptor-3-read-this-if-bats-hangs at bats-core/bats-core#176

README.md

@@ -367,7 +367,7 @@ service that will run indefinitely), Bats will be similarly blocked for the same
 amount of time.
 
 **To prevent this from happening, close FD 3 explicitly when running any command
-that may launch long-running child processes**, e.g. `command_name 3>- &`.
+that may launch long-running child processes**, e.g. `command_name 3>&-` .
 
 ### Printing to the terminal