Update .gitignore (#1291)

Ignore new `.idea` subdirectory generated by IDE, described in https://confluence.jetbrains.com/display/IDEADEV/New+project+code+style+settings+format+in+2017.3

Author: raphkim

.gitignore

@@ -43,6 +43,7 @@ captures/
 .idea/dictionaries
 .idea/libraries
 .idea/caches
+.idea/codeStyles
 .idea/misc.xml
 
 # Keystore files