FindBugs fix; Windows build fix.

[cameronxm]

FindBugs flagged access to a static field from a non-static context; introduced reference updater class and singleton instance. Also added a small change to make the tests work on Windows. (Since Windows is not a sufficiently enterprise platform, you may regard this part of the PR as optional.)

[codecov-io]

Current coverage is 89.56% (diff: 83.33%)

Merging #271 into master will increase coverage by 4.36%

@@             master       #271   diff @@
==========================================
  Files            61         61          
  Lines           358        345    -13   
  Methods           0          0          
  Messages          0          0          
  Branches         21         21          
==========================================
+ Hits            305        309     +4   
+ Misses           46         29    -17   
  Partials          7          7          

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[emiln]

Hi, @cameronxm, and thank you for your interest in FizzBuzzEnterpriseEdition. We are very excited about the proposed changes, but a few things need addressing before we can merge:

1. The indentation in the changes seems to be a mixture of tabs and spaces, which has sent several senior developers into a frothing rage. Line 28 in the file src/main/java/com/seriouscompany/business/java/fizzbuzz/packagenamingpackage/impl/ApplicationContextHolder.java was found particularly egregious, and our senior Spring developer, Tim, flat out refuses to merge the changes before this is fixed.
2. Business has for reasons that elude regular developers taken to a new obsession about code coverage and has descended upon all decreases with a blind zeal that leaves absolutely no wiggle room.I would suggesting adding superfluous, covered lines until the changeset in this PR becomes a net gain in total code coverage. It seems unlikely that business will be reasonable about the matter.

I hope we can quickly fix these trifles and see your great changes make it into the project.