ignore .checkstyle (#11)

diff --git a/.gitignore b/.gitignore
index 19e9e0b..8dc41a7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,4 +11,5 @@
 .idea
 .surefire-*
 .DS_Store
+.checkstyle
 *.versionsBackup