Add diff --unified option

[cohalz]

Enabled to display unified format like git diff.
It makes it easier to see if there are any unintended changes.

cohalz@co ecspresso % ./cmd/ecspresso/ecspresso diff --config=ecspresso.yml --unified
--- arn:aws:ecs:ap-northeast-1:123456789012:service/my-cluster/my-service
+++ ecs-service-def.json
@@ -7,7 +7,7 @@
     "maximumPercent": 200,
     "minimumHealthyPercent": 100
   },
-  "desiredCount": 1,
+  "desiredCount": 2,
   "enableExecuteCommand": true,
   "healthCheckGracePeriodSeconds": 0,
   "networkConfiguration": {

--- arn:aws:ecs:ap-northeast-1:123456789012:task-definition/my-tesk-definition:1
+++ ecs-task-def.json
@@ -44,7 +44,7 @@
     {
       "cpu": 0,
       "environment": [],
-      "essential": true,
+      "essential": false,
       "image": "nginx:latest",
       "linuxParameters": {
         "initProcessEnabled": true

[fujiwara]

Great feature! Thanks!!!