Add echo to stack.yaml

stack.yaml

@@ -10,6 +10,7 @@ extra-deps:
 - base64-bytestring-1.0.0.1
 - clock-0.7.2
 - cryptohash-sha256-0.11.100.1
+- echo-0.1.2
 - ed25519-0.0.5.0
 - edit-distance-0.2.2.1
 - exceptions-0.8.2.1