Makefile: Improved MacOS compatibility

[cannarelladev]

Description

In this PR I want to improve the Makefile compatibility with MacOS:

sed command in MacOS has a different behavior from the GNU one, in particular when it is used with the -i flag it needs a suffix for the name of the "backup" original file.

With this little fix it automatically selects the right sed syntax checking the running OS

[adamjensenbot]

Hi @cannarelladev. Thanks for your PR!

I am @adamjensenbot.
You can interact with me issuing a slash command in the first line of a comment.
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  when the rebase operation is completed)
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Make sure this PR appears in the liqo changelog, adding one of the following labels:

• kind/breaking: 💥 Breaking Change
• kind/feature: 🚀 New Feature
• kind/bug: 🐛 Bug Fix
• kind/cleanup: 🧹 Code Refactoring
• kind/docs: 📝 Documentation

[cheina97]

lgtm

[cheina97]

/rebase test=true

[cheina97]

/merge