fix: fix git show command

Previously the show command would also output the patch, and we'd run that through commitlint - it's
not super problematic but it's definitely not correct either.

src/index.js

@@ -61,7 +61,7 @@ async function lint(args, options) {
 }
 
 async function rawCommit(hash) {
-  const result = await execa('git', ['show', '--pretty=format:%B', hash]);
+  const result = await execa('git', ['show', '-s', '--pretty=format:%B', hash]);
   return result.stdout;
 }