read user input when script is passed through a pipe. closes #687

Author: gbourant

src/std/env.ab

@@ -64,7 +64,7 @@ pub fun is_command(command: Text): Bool {
 
 /// Creates a prompt and returns the value.
 pub fun input_prompt(prompt: Text): Text {
-    trust $ read -p "\${nameof prompt}" $
+    trust $ read -p "\${nameof prompt} < /dev/tty" $
     return "\$REPLY"
 }