ignore .checkstyle file from eclipse (#15)

diff --git a/.gitignore b/.gitignore
index 5006e87..3a77bd2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 .classpath
 .project
 .settings
+.checkstyle
 #idea
 *.iml
 .idea