Bumping to Go 1.15

[jmrodri]

Description of the change:
Bumping go from 1.13 to 1.15 in go.mod.

Motivation for the change:
Moving to Go 1.15 like we did for operator-sdk: https://github.com/operator-framework/operator-sdk/blob/master/go.mod#L3

[coveralls]

Pull Request Test Coverage Report for Build 366310051

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 75.921%

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Totals
Change from base Build 306912882:	0.0%
Covered Lines:	268
Relevant Lines:	353

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💛 - Coveralls

[camilamacedo86]

After update the CI:

operator-lib/.github/workflows/ci.yml

Line 19 in aac7eed

go-version: ^1.13

/lgtm

[joelanford]

/approve

But can we go ahead and bump the line that @camilamacedo86 mentioned in this PR? Feel free to remove the hold once the github action workflow is updated to 1.15.
/hold

In addition to that one, we also need to update the base image for the openshift/release job.

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: joelanford

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[jmrodri]

/hold cancel

[joelanford]

/lgtm