fix (adb): shell to return expected stdout

[erisu]

Motivation and Context

Fix error when executing cordova run android to launch app in emulator.

Description

When executing cordova run android to launch the app in an emulator, the Adb.shell method does not return the expected stdout anymore and results in the following error

output.match is not a function

This bug was introduced during the execa refactor.

Testing

• npm t
• cordova run android

Checklist

• I've run the tests to see all new and existing tests pass

[codecov-io]

Codecov Report

Merging #904 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #904      +/-   ##
==========================================
+ Coverage   66.17%   66.19%   +0.01%     
==========================================
  Files          19       19              
  Lines        1839     1840       +1     
==========================================
+ Hits         1217     1218       +1     
  Misses        622      622

Impacted Files	Coverage Δ
bin/templates/cordova/lib/Adb.js	100% <100%> (ø)	⬆️

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[breautek]

Confirmed the issue on master, and confirmed that this PR fixes the issue.