fix gatling 3 launcher generation for windows

[nichero-h]

Fix gatling-launcher.bat generation.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (573aeca) 89.06% compared to head (add7c0c) 89.06%.

Files	Patch %	Lines
bzt/modules/gatling.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1786      +/-   ##
==========================================
+ Coverage   89.06%   89.06%   +0.01%     
==========================================
  Files          70       70              
  Lines       19003    19003              
==========================================
+ Hits        16923    16924       +1     
+ Misses       2080     2079       -1     

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