Updated incorrect installation URL in Analytics-Go documentation

[neelkanth-kaushik]

Problem Statement

Running go get gopkg.in/segmentio/analytics-go.v3 is giving following error:

go: gopkg.in/segmentio/analytics-go.v3@upgrade (v3.3.0) requires gopkg.in/segmentio/analytics-go.v3@v3.3.0: parsing go.mod:
        module declares its path as: github.com/segmentio/analytics-go/v3
                but was required as: gopkg.in/segmentio/analytics-go.v3

Changes

1. Replaced go get gopkg.in/segmentio/analytics-go.v3 with go get github.com/segmentio/analytics-go/v3
2. Replaced import "gopkg.in/segmentio/analytics-go.v3" with import "github.com/segmentio/analytics-go/v3"
3. Removed Alternatively, you can also use gopkg.in. First run go get gopkg.in/segmentio/analytics-go.v3 and replace your imports with import "gopkg.in/segmentio/analytics-go.v3".

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