set window focus fix

[ashdo]

Fixes #326.

Existing hook sets focus to some window, but it does not set the focus back to the last (previously selected) window, but to the previous window (previous in the list of windows in the session).

My commit fixes this without any deeper knowledge about the hook itself.

Unfortunately the hook tells "no last window" to me now.

[codecov-io]

Codecov Report

Merging #473 into master will decrease coverage by 0.12%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #473      +/-   ##
==========================================
- Coverage   75.06%   74.93%   -0.13%     
==========================================
  Files           5        5              
  Lines         794      794              
  Branches      231      231              
==========================================
- Hits          596      595       -1     
  Misses        146      146              
- Partials       52       53       +1

Impacted Files	Coverage Δ
tmuxp/cli.py	56.23% <100%> (ø)	⬆️
tmuxp/workspacebuilder.py	90.9% <0%> (-0.61%)	⬇️

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[sluther]

I can confirm that the above fix works for me. In addition, it seems that the Travis CI check failed due to network error.

[anselmos]

It has been fixed in #500 @sluther - you may close this PR :)

[tony]

Thank you @anselmos

@ashdo : I'm closing this PR for now since #500 is live as of 1.5.4

If this persists please feel free to reopen