Use try-with-resources instead closeQuietly

[malaskowski]

Description

Use try-with-resources instead closeQuietly to close StringReader.

Motivation and Context

In Vert.x 3.9.1 closeQuietly was removed, see https://github.com/vert-x3/vertx-config/pull/115.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] I have read the CONTRIBUTING document.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.

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I hereby agree to the terms of the Knot.x Contributor License Agreement.

[codecov[bot]]

Codecov Report

Merging #38 into master will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master      #38   +/-   ##
=========================================
  Coverage     80.35%   80.35%           
  Complexity      153      153           
=========================================
  Files            17       17           
  Lines           616      616           
  Branches         30       30           
=========================================
  Hits            495      495           
  Misses          105      105           
  Partials         16       16           

Impacted Files	Coverage Δ	Complexity Δ
...n/java/io/knotx/launcher/config/ConfProcessor.java	63.41% <100.00%> (ø)	4.00 <1.00> (ø)

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