fix: do not use a shell for git commands

Author: nlf

Diff for: lib/opts.js

@@ -7,5 +7,6 @@ const gitEnv = {
 module.exports = (opts = {}) => ({
   stdioString: true,
   ...opts,
+  shell: false,
   env: opts.env || { ...gitEnv, ...process.env }
 })

Diff for: test/opts.js

@@ -7,6 +7,9 @@ const gitEnv = {
 
 t.match(gitOpts().env, gitEnv, 'got the git defaults we want')
 
+t.equal(gitOpts().shell, false, 'shell defaults to false')
+t.equal(gitOpts({ shell: '/bin/bash' }).shell, false, 'shell cannot be overridden')
+
 t.test('does not override', t => {
   const { GIT_ASKPASS, GIT_SSH_COMMAND } = process.env
   t.teardown(() => {