fix: watch.stream stores resource_version for the next call

[tomplus]

The method Watch.Stream stores a resource version to use in the next calls if the first hasn't returned another value.

Fixes #77

[codecov-io]

Codecov Report

Merging #89 into master will increase coverage by 0.01%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   93.54%   93.55%   +0.01%     
==========================================
  Files          23       23              
  Lines        1533     1551      +18     
==========================================
+ Hits         1434     1451      +17     
- Misses         99      100       +1

Impacted Files	Coverage Δ
kubernetes_asyncio/watch/watch.py	93.4% <100%> (+0.14%)	⬆️
kubernetes_asyncio/watch/watch_test.py	95.65% <93.75%> (-0.31%)	⬇️

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