Fixed error message capitalization

[cushonz]

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• The PR follows
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

What kind of change does this PR introduce?

Simple syntax changes to error messages.

What is the current behavior?

Currently the message is incorrectly capitalized.

What is the new behavior?

Corrects capitalization on all "Libraries: " strings to "libraries: "

Does this PR introduce a breaking change, and is titled accordingly?

No, the changes made in this pull request are trivial and should not impact operation

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Base: 36.55% // Head: 36.55% // No change to project coverage 👍

Coverage data is based on head (7093067) compared to base (a58d5ad).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2048   +/-   ##
=======================================
  Coverage   36.55%   36.55%           
=======================================
  Files         229      229           
  Lines       19383    19383           
=======================================
  Hits         7085     7085           
  Misses      11462    11462           
  Partials      836      836           

Flag	Coverage Δ
unit	36.55% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/cli/lib/list.go	0.00% <0.00%> (ø)
commands/lib/search.go	88.15% <0.00%> (-3.95%)	⬇️
arduino/cores/packagemanager/package_manager.go	66.58% <0.00%> (+0.75%)	⬆️

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