fix run-server.sh volume path in Cygwin

[kevinAlbs]

To fix an observed error running run-server.sh with a Cygwin shell:

/root/base-entrypoint.sh: line 10: cd: /root/drivers-evergreen-tools/.evergreen:
 No such file or directory

The error appears caused by the Unix-style path in the host path of the -v argument. This PR changes the host path to Windows-style.

Example before:

-v /cygdrive/c/code/drivers-evergreen-tools:/root/drivers-evergreen-tools

Example after:

-v C:\code\drivers-evergreen-tools:/root/drivers-evergreen-tools

https://docs.docker.com/reference/cli/docker/container/run/#volume notes:

On Windows, you must specify the paths using Windows-style path semantics.