Tell Git to use LF eol for .sh files

Without this, `vagrant up` fails on Windows:

    containerd-linux: /tmp/vagrant-shell: ./setup.sh: /bin/bash^M: bad interpreter: No such file or directory
    The SSH command responded with a non-zero exit status. Vagrant
    assumes that this means the command failed. The output for this command
    should be in the log above. Please read the output to determine what
    went wrong.

.gitattributes

@@ -0,0 +1 @@
+*.sh text eol=lf