Change xargs command for mac and increase fees

[shawnlimjunhe]

This PR addresses a compatibility issue I found when trying to run the deploy script. The xargs command seems to fail on macOS.

Issue Background

While following the tutorial, I add trouble executing the deploy script on my Macbook. After investigating, I found that the issue originates from: 1) the xargs command and 2) the low fees in the wasm instantiate command

Proposed solution

I have modified the deployment script to detect the OS and if it's mac, use the sed command instead to trim whitespaces. I also increased the fees amount to fix the following error:
raw_log: '[{"log":"insufficient fees; got: 300000usei required: 3000000usei: insufficient fee"}]