Update introduction.md

Programming Go
1

Fix typo in name of variable

2

Do you have some more context or a link to what you’re meaning?

3

I assume it’s this: Update introduction.md by u-mulder · Pull Request #2744 · exercism/go · GitHub

This fixes a typo in a variable name in the intro markdown in a code example.

4

See also:

+cc @andrerfcsantos @junedev