add intellij files to ignore (#510)

diff --git a/.gitignore b/.gitignore
index d6952bc..dbd7421 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,5 @@
 !org.jacoco.core/.settings/
 !org.jacoco.core.test/.settings/
 org.jacoco.agent/src/jacocoagent.jar
+.idea
+*.iml