Pin golang to avoid breakages.

[mattmoor]

Changes

/kind bug

Pin the version of Go to fix the Dockerfile build.

I see the following prior to this change:

        E0217 14:26:03.966047      12 aws_credentials.go:77] while getting AWS credentials NoCredentialProviders: no valid providers in chain. Deprecated.
        	For verbose messaging see aws.Config.CredentialsChainVerboseErrors
        INFO[0000] Retrieving image manifest golang             
        INFO[0000] Retrieving image golang                      
        INFO[0000] Retrieving image manifest golang             
        INFO[0000] Retrieving image golang                      
        INFO[0001] Built cross stage deps: map[]                
        INFO[0001] Retrieving image manifest golang             
        INFO[0001] Retrieving image golang                      
        INFO[0001] Retrieving image manifest golang             
        INFO[0001] Retrieving image golang                      
        INFO[0001] Executing 0 build triggers                   
        INFO[0001] Unpacking rootfs as cmd COPY . /go/src/github.com/tektoncd/pipeline/ requires it. 
        INFO[0029] COPY . /go/src/github.com/tektoncd/pipeline/ 
        INFO[0033] Taking snapshot of files...                  
        INFO[0036] RUN go install github.com/tektoncd/pipeline/test/gohelloworld 
        INFO[0036] Taking snapshot of full filesystem...        
        INFO[0044] cmd: /bin/sh                                 
        INFO[0044] args: [-c go install github.com/tektoncd/pipeline/test/gohelloworld] 
        INFO[0044] Running: [/bin/sh -c go install github.com/tektoncd/pipeline/test/gohelloworld] 
        go install: version is required when current directory is not in a module
        	Try 'go install github.com/tektoncd/pipeline/test/gohelloworld@latest' to install the latest version
        error building image: error building stage: failed to execute command: waiting for process to exit: exit status 1

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Release Notes

NONE

/assign @afrittoli @vdemeester @imjasonh

[afrittoli]

Thank you!
/approve

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: afrittoli

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[AlanGreene]

/lgtm

[afrittoli]

/lgtm