[108] eliminate tests skipping on windows

[Doldrums]

Case is the following:

There are several tests ignored on windows, e.g. test_reads_git_author. These tests are ignored via "skip if Gem.win_platform?" but this makes it very difficult to develop, since you can not run the entire test suite.
Imho these tests should not be ignored and should be fixed.

May notice that there are not much strong differences in the commands for the terminal and Windows console; so we can correct this situation

[Doldrums]

Perhaps more specific comments are needed:

• the only difference is in the structure of these terminal command tests
• if you evaluate in detail what is being executed there: the error can only be on set -e
• The ERRORLEVEL is already set, so there is no need to GOTO a label that sets the ERRORLEVEL.

[yegor256]

@Doldrums can you please first help with this #204?

[Doldrums]

@yegor256 sure