Adds bash shebang to execute.sh script

This commit adds the bash shebang allowing to execute the script without guess the right interpreter

Author: claudiopastorini

scripts/execute.sh

@@ -1,3 +1,4 @@
+#!/bin/bash
 # config
 STACK_NAME=lambda-power-tuning
 INPUT=$(cat scripts/sample-execution-input.json)  # or use a static string
@@ -32,4 +33,4 @@ do
         aws stepfunctions describe-execution --execution-arn $EXECUTION_ARN --query 'output' --output text
         break
     fi
-done
+done