chore: update copyright year to 2021

[jbrockopp]

This is a general housekeeping task.

I used VS code's search and replace:

• Search: Copyright (c) 2020
• Replace: Copyright (c) 2021

At the top of every file, the new copyright statement now looks like:

// Copyright (c) 2021 Target Brands, Inc. All rights reserved.

[codecov]

Codecov Report

Merging #54 (67d121f) into master (4736cc8) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master      #54   +/-   ##
=======================================
  Coverage   36.61%   36.61%           
=======================================
  Files           7        7           
  Lines         183      183           
=======================================
  Hits           67       67           
  Misses         98       98           
  Partials       18       18           

Impacted Files	Coverage Δ
cmd/secret-vault/config.go	53.84% <ø> (ø)
cmd/secret-vault/flag.go	0.00% <ø> (ø)
cmd/secret-vault/main.go	0.00% <0.00%> (ø)
cmd/secret-vault/plugin.go	25.00% <ø> (ø)
cmd/secret-vault/read.go	70.58% <ø> (ø)
vault/read.go	33.33% <ø> (ø)
vault/vault.go	56.41% <ø> (ø)

[KellyMerrick]

lgtm