Added check for old working copy

[edgardmessias]

If working copy is old (Ex. 1.6) and the client is new (Ex. 1.9), show a prompt to upgrade the working copy

[codecov]

Codecov Report

Merging #306 into master will decrease coverage by 0.2%.
The diff coverage is 9.09%.

@@            Coverage Diff             @@
##           master     #306      +/-   ##
==========================================
- Coverage   61.38%   61.18%   -0.21%     
==========================================
  Files          38       38              
  Lines        2574     2607      +33     
  Branches      466      474       +8     
==========================================
+ Hits         1580     1595      +15     
- Misses        987     1005      +18     
  Partials        7        7

Impacted Files	Coverage Δ
src/svn.ts	78.21% <0%> (-2.6%)	⬇️
src/model.ts	66.07% <16.66%> (-2.76%)	⬇️
src/commands.ts	50.08% <5.26%> (-1.51%)	⬇️
src/repository.ts	67.69% <0%> (+1.53%)	⬆️
src/statusBar.ts	79.48% <0%> (+2.56%)	⬆️
src/statusParser.ts	92.1% <0%> (+15.78%)	⬆️

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[edgardmessias]

Ping @JohnstonCode