Fix require github.com/gocolly/colly/v2: version "latest" invalid: must be of the form v1.2.3

[youngjuning]

[JDRanpariya]

Gotcha I hope someone allow this PR to get merged ASAP

[WGH-]

Where this error comes from? I'm pretty sure github.com/gocolly/colly/v2 latest gets automatically replaced by all Go tools:

$ go build 
go: updates to go.mod needed; to update it:
	go mod tidy
$ go mod tidy
$ cat go.mod
module lkjdsgds

go 1.13

require github.com/gocolly/colly/v2 v2.1.0

With that said, I think this instruction should be replaced with go get github.com/gocolly/colly/v2@latest.