Add pre commit hook for ktlint

gradle/kotlin/hooks/ktlint-git-pre-commit-hook.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+# https://github.com/shyiko/ktlint pre-commit hook
+
+git diff --name-only --relative | grep '\.kt[s"]\?$' | xargs ktlint --relative .
+if [ $? -ne 0 ]; then exit 1; fi