fix: fix wrong import module path

[ColeDrain]

• fix wrong import for in main.go
• change import path for go-zopfli

[ColeDrain]

discussion: I see one of the goals of this project is: "We aim for simplicity with the least external dependencies"

Do we plan on adding the go-zopfli library directly to the project ?

[kislerdm]

Do we plan on adding the go-zopfli library directly to the project ?

I'd like to suggest to follow the status quo: please consider the comment for the context. We can re-evaluate the decision at a later point. Thanks!