fix debug env

[moritzraho]

Description

let debugLogger = require('@adobe/aio-lib-core-logging')('App', {provider:'debug'})
debugLogger.error('blabla')

returns App:error blabla while the DEBUG environment variable is not set

This leads to unexpected behaviours, for example in aio-lib-state, aio-lib-files and aio-lib-core-tvm an error will be always displayed, while libraries shouldn’t log anything by default.

This PR fixes this by making sure that the debug logger only shows logs if the DEBUG env var is set

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov[bot]]

Codecov Report

Merging #26 into master will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #26   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           90        92    +2     
  Branches        12        12           
=========================================
+ Hits            90        92    +2     

Impacted Files	Coverage Δ
src/DebugLogger.js	100.00% <100.00%> (ø)

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