fix: use ':' instead of '=' for esbuild 'define' argument

[mattsoulanille]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

esbuild passes global definitions as --define=the_var=value instead of --define:the_var=value as documented.
Issue Number: N/A

What is the new behavior?

Pass global definitions as --define:the_var=value.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[mattsoulanille]

I think there's a similar bug with --external. I can create a PR for it as well.

[mattem]

Thanks! Yeah if you are able to submit a PR for --external too that would be great